**4. Metal ion implantation into GaN**

Cobalt ions were implanted into GaN at doses of 3 × 1016 and 5 × 1016 ions cm−2 and chromium ions were implanted at a dose of 3 × 1016 ions cm−2.

#### **4.1. Cobalt implantation into GaN**

### *4.1.1. X‐ray diffraction (XRD)*

Typical XRD spectra of GaN for as-grown and all the implanted samples annealed at 700, 800 and 900°C are given in **Figures 10** and **11**. **Figures 10** and **11** show typical XRD profiles of Co<sup>+</sup> implanted GaN at 3 × 1016 and 5 × 1016 ions cm−2 and subsequently annealed at 700, 800 and 900°C. In the as-grown sample, three main peaks appeared corresponding to the expected diffraction from the GaN epilayer and sapphire substrate structure.

Comparison of the XRD patterns of the as-grown with the implanted samples at different doses, it can be observed that no secondary phases or metal-related peaks were detected in the as-implanted samples and annealed samples. The diffraction patterns show peaks corresponding to the GaN layer and the substrate structure only. However, the presence of sufficiently small cobalt nanoscale precipitates, which cannot be detected by XRD due to its insensitivity on the nanoscale [43, 44], is possible.

HR-XRD (*θ* − 2*θ*) spectra showing the (0002) peak of GaN for the as-grown and selected implanted samples at doses 3 × 1016 and 5 ×1016 ions cm−2 and annealed at 900°C are given in **Figures 12** and **13**. In **Figure 12**, the diffraction pattern of the implanted sample, a typical satellite peak appears at lower side of the main GaN (0002) reflection. Ion implantation into crystalline GaN introduces lattice disorder which is a side effect of implantation [4]. As a result, in addition to GaN peak, new peak/peaks, representing the damaged part of lattice, appear on the low angle side of the main GaN peak in the XRD spectra of implanted GaN as reported by many researchers [45–49].

The shape, position and number of such new peaks were found to differ for different ions implanted into GaN. Most of the authors attributed such new XRD peaks to the implantation induced strain and the expansion of GaN lattice in the implanted portion of the material [45–48]. Another group of researchers suggested that these peaks were related to the formation of new phases [49]. Liu et al. presented a comparative XRD study of Ca- and Ar-implanted GaN and observed larger lattice expansion for Ar implantation. They assigned the observed phenomenon to the inability of inert gas ions to occupy substitutional sites in the lattce [45]. Inert gases, due to their very low solubility in solids, are reported to produce small gas-vacancy clusters that lead to the formation of gas-filled cavities called bubbles [50]. The formation of such inert gas cavities was also observed in several other materials such as Si [51], GaAs [52], SiC [53] and InP [54]. These empty cavities, due to their negative curvatures, contain high density of dangling bonds that exhibit high affinity for metallic contaminants and can act as impurity gettering sites [55]. Gettering of oxygen impurity atoms and structural defects in GaN by helium implantation has been reported [55–57].

**Figure 10.** Typical XRD pattern of Co+ implanted at dose 3 × 10<sup>16</sup> cm−2 [66].

**4. Metal ion implantation into GaN**

**4.1. Cobalt implantation into GaN**

*4.1.1. X‐ray diffraction (XRD)*

26 Ion Implantation - Research and Application

ions were implanted at a dose of 3 × 1016 ions cm−2.

insensitivity on the nanoscale [43, 44], is possible.

by helium implantation has been reported [55–57].

reported by many researchers [45–49].

diffraction from the GaN epilayer and sapphire substrate structure.

Cobalt ions were implanted into GaN at doses of 3 × 1016 and 5 × 1016 ions cm−2 and chromium

Typical XRD spectra of GaN for as-grown and all the implanted samples annealed at 700, 800 and 900°C are given in **Figures 10** and **11**. **Figures 10** and **11** show typical XRD profiles of Co<sup>+</sup> implanted GaN at 3 × 1016 and 5 × 1016 ions cm−2 and subsequently annealed at 700, 800 and 900°C. In the as-grown sample, three main peaks appeared corresponding to the expected

Comparison of the XRD patterns of the as-grown with the implanted samples at different doses, it can be observed that no secondary phases or metal-related peaks were detected in the as-implanted samples and annealed samples. The diffraction patterns show peaks corresponding to the GaN layer and the substrate structure only. However, the presence of sufficiently small cobalt nanoscale precipitates, which cannot be detected by XRD due to its

HR-XRD (*θ* − 2*θ*) spectra showing the (0002) peak of GaN for the as-grown and selected implanted samples at doses 3 × 1016 and 5 ×1016 ions cm−2 and annealed at 900°C are given in **Figures 12** and **13**. In **Figure 12**, the diffraction pattern of the implanted sample, a typical satellite peak appears at lower side of the main GaN (0002) reflection. Ion implantation into crystalline GaN introduces lattice disorder which is a side effect of implantation [4]. As a result, in addition to GaN peak, new peak/peaks, representing the damaged part of lattice, appear on the low angle side of the main GaN peak in the XRD spectra of implanted GaN as

The shape, position and number of such new peaks were found to differ for different ions implanted into GaN. Most of the authors attributed such new XRD peaks to the implantation induced strain and the expansion of GaN lattice in the implanted portion of the material [45–48]. Another group of researchers suggested that these peaks were related to the formation of new phases [49]. Liu et al. presented a comparative XRD study of Ca- and Ar-implanted GaN and observed larger lattice expansion for Ar implantation. They assigned the observed phenomenon to the inability of inert gas ions to occupy substitutional sites in the lattce [45]. Inert gases, due to their very low solubility in solids, are reported to produce small gas-vacancy clusters that lead to the formation of gas-filled cavities called bubbles [50]. The formation of such inert gas cavities was also observed in several other materials such as Si [51], GaAs [52], SiC [53] and InP [54]. These empty cavities, due to their negative curvatures, contain high density of dangling bonds that exhibit high affinity for metallic contaminants and can act as impurity gettering sites [55]. Gettering of oxygen impurity atoms and structural defects in GaN

**Figure 11.** Typical XRD pattern of Co+ implanted at dose 5 × 10<sup>16</sup> cm−2 [67].

**Figure 12.** HR-XRD pattern of Co+ implanted at 3 × 10<sup>16</sup> ions cm−2 [66].

**Figure 13.** HR-XRD pattern of Co+ implanted at 5 × 10<sup>16</sup> ions cm−2 [67].

The presence of similar peaks has previously been observed in the XRD spectra of GaN implanted with different ions and is thought to be due to lattice expansion along the *c*-axis of GaN [45, 46]. The new peak from HR-XRD measurements is attributed to implantationinduced damage and also to the formation of Ga1-*<sup>x</sup>* Co*<sup>x</sup>* N on the part of the sample which was implanted. A shoulder peak observed on the left side of the GaN peak on XRD scans of MBE grown samples has been attributed to the GaMnN phase by Cui and Li [58]. The lattice constant of (Ga,Co)N varies with cobalt incorporation, implying that the position of the new peak is related to the amount of cobalt in the material. Hence, the introduction of cobalt at interstitial and substitutional sites in GaN is expected to cause lattice expansion to produce a new XRD peak on the left side of the GaN peak [59]. The shifting of additional peaks to the right with annealing, presented in both **Figures 12** and **13**, points to lattice recovery and improvement in the uniformity of GaCoN which may be due to increase in the substitution probability of cobalt atoms.

#### *4.1.2. RBS channelling*

**Figure 13.** HR-XRD pattern of Co+ implanted at 5 × 10<sup>16</sup> ions cm−2 [67].

**Figure 12.** HR-XRD pattern of Co+ implanted at 3 × 10<sup>16</sup> ions cm−2 [66].

28 Ion Implantation - Research and Application

The RBS channelling spectrum of the as-grown GaN/sapphire (0001) together with the corresponding minimum channelling yield *χ*min = 1.3%, indicating high crystalline quality [60, 61], is shown in **Figure 14**.

**Figure 14.** RBS/C of as-grown sample along with the backscattering geometry [66].

A random spectrum simulation was carried out using the RUMP program [62]. Channelling spectra are presented in **Figures 15** and **16** for Co+ implanted GaN sample at doses of 3 × 1016 and 5 × 1016 ions cm−2 and subsequently annealed samples at 700, 800 and 900°C along with the corresponding minimum channelling yields *χ*min. **Figures 15** and **16** present minimum channelling yields *χ*min calculated for the maximum at around 1.64 MeV and is related to the random spectrum of virgin (upper spectrum) GaN.

The random spectrum of the as-implanted GaN is not shown here due to minor differences with the random spectrum of as-grown GaN. Co<sup>+</sup> implanted GaN sample at doses 3 × 1016 and 5 × 1016 ions cm−2 and subsequently annealed at 900°C showed better recovery of implantation damage. From our measurements, annealing at 900°C is the most suitable annealing temperature to re-crystallize the samples.

#### *4.1.3. AGM and SQUID*

Magnetization against magnetic field (M-H) curves from AGM measurements at room temperature for the samples implanted at doses of 3 × 1016 and 5 × 1016 ions cm−2 and subsequently annealed at 700, 800 and 900°C are shown in **Figures 17** and **18**, where the signal from the sapphire substrate (diamagnetic) was extracted. The magnetic field was applied parallel to the sample plane. Well-defined hysteresis loops were observed even at 300 K. The saturation field was about 4000 Oe and the coercivity *H*<sup>c</sup> was about 100 Oe for the implanted and annealed samples. These results confirm that the samples were ferromagnetic even at room temperature.

**Figure 15.** RBS/C of Co+ implanted GaN at 3 × 10<sup>16</sup> ions cm−2 and annealed samples at different temperatures [66].

**Figure 16.** RBS/C of Co+ implanted GaN at 5 × 10<sup>16</sup> ions cm−2 and annealed samples at different temperatures [67].

**Figure 17.** M-H loops at 300 K of sample implanted at dose 3 × 10<sup>16</sup> ions cm−2 and annealed [66].

**Figure 15.** RBS/C of Co+ implanted GaN at 3 × 10<sup>16</sup> ions cm−2 and annealed samples at different temperatures [66].

A random spectrum simulation was carried out using the RUMP program [62]. Channelling

and 5 × 1016 ions cm−2 and subsequently annealed samples at 700, 800 and 900°C along with the corresponding minimum channelling yields *χ*min. **Figures 15** and **16** present minimum channelling yields *χ*min calculated for the maximum at around 1.64 MeV and is related to the

The random spectrum of the as-implanted GaN is not shown here due to minor differences

5 × 1016 ions cm−2 and subsequently annealed at 900°C showed better recovery of implantation damage. From our measurements, annealing at 900°C is the most suitable annealing tempera-

Magnetization against magnetic field (M-H) curves from AGM measurements at room temperature for the samples implanted at doses of 3 × 1016 and 5 × 1016 ions cm−2 and subsequently annealed at 700, 800 and 900°C are shown in **Figures 17** and **18**, where the signal from the sapphire substrate (diamagnetic) was extracted. The magnetic field was applied parallel to the sample plane. Well-defined hysteresis loops were observed even at 300 K. The satura-

annealed samples. These results confirm that the samples were ferromagnetic even at room

implanted GaN sample at doses of 3 × 1016

implanted GaN sample at doses 3 × 1016 and

was about 100 Oe for the implanted and

spectra are presented in **Figures 15** and **16** for Co+

random spectrum of virgin (upper spectrum) GaN.

with the random spectrum of as-grown GaN. Co<sup>+</sup>

tion field was about 4000 Oe and the coercivity *H*<sup>c</sup>

ture to re-crystallize the samples.

30 Ion Implantation - Research and Application

*4.1.3. AGM and SQUID*

temperature.

**Figure 18.** M-H loops at 300 K of sample implanted at dose 5 × 10<sup>16</sup> ions cm−2 and annealed [67].

Similarly, a well-defined hysteresis loop, measured using a SQUID magnetometer, at 5 K was also observed from samples implanted at a dose of 3 × 10<sup>16</sup> ions cm−2 and subsequently annealed at 700, 800 and 900°C as shown in **Figure 19**. The saturation field was about 4000 Oe and the coercivity *H*<sup>c</sup> was about 180 Oe for implanted and annealed samples at 700 and 800°C and the coercivity was observed around 270 Oe for the sample annealed at 900°C. Also, a well-defined hysteresis loop at 5 K from SQUID was also observed for the samples implanted at a dose of 5 ×1016 ions cm−2 and subsequently annealed at 700, 800 and 900°C as shown in **Figure 20**. The saturation field was about 4000 Oe and the coercivity *Hc* was about 270 Oe for implanted and annealed samples at 700 and 800°C and the coercivity was observed around 600 Oe for the sample annealed at 900°C.

**Figure 19.** M-H loops at 5 K of sample implanted at dose 3 × 10<sup>16</sup> ions cm−2 and annealed [66].

**Figure 20.** M-H loops at 5 K of sample implanted at dose 5 × 10<sup>16</sup> ions cm−2 and annealed [67].

**Figure 18.** M-H loops at 300 K of sample implanted at dose 5 × 10<sup>16</sup> ions cm−2 and annealed [67].

and the coercivity *H*<sup>c</sup>

32 Ion Implantation - Research and Application

600 Oe for the sample annealed at 900°C.

Similarly, a well-defined hysteresis loop, measured using a SQUID magnetometer, at 5 K was also observed from samples implanted at a dose of 3 × 10<sup>16</sup> ions cm−2 and subsequently annealed at 700, 800 and 900°C as shown in **Figure 19**. The saturation field was about 4000 Oe

and the coercivity was observed around 270 Oe for the sample annealed at 900°C. Also, a well-defined hysteresis loop at 5 K from SQUID was also observed for the samples implanted at a dose of 5 ×1016 ions cm−2 and subsequently annealed at 700, 800 and 900°C as shown in **Figure 20**. The saturation field was about 4000 Oe and the coercivity *Hc* was about 270 Oe for implanted and annealed samples at 700 and 800°C and the coercivity was observed around

was about 180 Oe for implanted and annealed samples at 700 and 800°C

**Figure 19.** M-H loops at 5 K of sample implanted at dose 3 × 10<sup>16</sup> ions cm−2 and annealed [66].

Magnetization as a function of temperature for selected samples is plotted in **Figures 21** and **22**. The variation of magnetization with temperature indicates multiple exchange interactions,

**Figure 21.** FC/ZFC measurements of sample implanted at a dose of 3 × 10<sup>16</sup> ions cm−2 and annealed at 900°C [66].

**Figure 22.** FC/ZFC measurements of sample implanted at a dose of 5 × 10<sup>16</sup> ions cm−2 and annealed at 900°C [67].

indicating that its decay cannot be easily fit to classical description of ferromagnetism, again in agreement with current theories concerning DMS systems with low carrier concentrations. Co+ implanted GaN at doses of 3 × 1016 and 5 × 1016 ions cm−2 and annealed at 900°C showed magnetic moment at lower temperatures and retained magnetization up to 370 K. There were indications of the possible presence of multiple complex exchange interactions for Co<sup>+</sup> implanted GaN. The same phenomenon has been observed on Cr<sup>+</sup> implanted GaN.

All samples exhibited well-saturated MH loops (**Figures 17**–**20**) with finite coercivity, eliminating the likelihood of both paramagnetism and superparamagnetism [63]. Analysing hysteresis loops of the implanted samples assists in the investigation of the magnetic properties of the material. Lateral shifting of hysteresis loop was not observed, and this eliminates spin glass behaviour [64]. These observations imply that there was ferromagnetic ordering in implanted samples at room temperature. No extra peaks were observed on the XRD spectra of the implanted samples (**Figures 10** and **11**), reducing the contributions of secondary phases (Co*<sup>x</sup>* N*y* , CoGa, etc.) to the observed ferromagnetism. FC and ZFC measurements were performed on a representative sample, together with magnetization as a function of temperature, and the data did not show any blocking temperature that can be related to superparamagnetic behaviour arising from undetected magnetic secondary phase clusters.

#### **4.2. Chromium implantation into GaN**

#### *4.2.1. X‐ray diffraction (XRD)*

Typical XRD spectra of GaN for the as-grown and Cr<sup>+</sup> implanted at a dose of 3 ×1016 ions cm−2 and subsequently annealed at 800 and 900°C are given in **Figure 23**. In the as-grown sample, the three main peaks correspond to the expected diffraction from the GaN epilayer and sapphire substrate structure.

**Figure 23.** Typical XRD pattern for the as-grown, implanted and annealed samples at different temperatures.

**Figure 22.** FC/ZFC measurements of sample implanted at a dose of 5 × 10<sup>16</sup> ions cm−2 and annealed at 900°C [67].

implanted GaN. The same phenomenon has been observed on Cr<sup>+</sup>

behaviour arising from undetected magnetic secondary phase clusters.

**4.2. Chromium implantation into GaN**

Typical XRD spectra of GaN for the as-grown and Cr<sup>+</sup>

*4.2.1. X‐ray diffraction (XRD)*

34 Ion Implantation - Research and Application

phire substrate structure.

Co+

(Co*<sup>x</sup>* N*y*

indicating that its decay cannot be easily fit to classical description of ferromagnetism, again in agreement with current theories concerning DMS systems with low carrier concentrations.

All samples exhibited well-saturated MH loops (**Figures 17**–**20**) with finite coercivity, eliminating the likelihood of both paramagnetism and superparamagnetism [63]. Analysing hysteresis loops of the implanted samples assists in the investigation of the magnetic properties of the material. Lateral shifting of hysteresis loop was not observed, and this eliminates spin glass behaviour [64]. These observations imply that there was ferromagnetic ordering in implanted samples at room temperature. No extra peaks were observed on the XRD spectra of the implanted samples (**Figures 10** and **11**), reducing the contributions of secondary phases

, CoGa, etc.) to the observed ferromagnetism. FC and ZFC measurements were performed on a representative sample, together with magnetization as a function of temperature, and the data did not show any blocking temperature that can be related to superparamagnetic

and subsequently annealed at 800 and 900°C are given in **Figure 23**. In the as-grown sample, the three main peaks correspond to the expected diffraction from the GaN epilayer and sap-

 implanted GaN at doses of 3 × 1016 and 5 × 1016 ions cm−2 and annealed at 900°C showed magnetic moment at lower temperatures and retained magnetization up to 370 K. There were indications of the possible presence of multiple complex exchange interactions for Co<sup>+</sup>

implanted GaN.

implanted at a dose of 3 ×1016 ions cm−2

XRD did not show any secondary phases or metal-related peaks on the as-implanted samples and annealed samples, when compared with the as-grown sample. Only peaks corresponding to the GaN layer and the substrate structure could be observed on the diffraction pattern. However, the presence of sufficiently small chromium nanoscale precipitates, which cannot be measured by typical XRD due to its insensitivity on the nanoscale [43, 44], is not excluded. HR-XRD spectra of GaN for implanted samples at a dose of 3 × 10<sup>16</sup> ions cm−2 and annealed at 900°C are given in **Figure 24**. In the diffraction pattern of the implanted sample, a typical satellite peak appears at the lower side of the main GaN (0002) reflection.

**Figure 24.** 2 HR-XRD spectra for Cr+ implanted GaN and subsequently annealed at 900°C [68].

The shape, position and number of such new peaks were found different as observed in Co<sup>+</sup> implanted GaN epilayers. The new peak in the XRD scans is assigned to implantation-induced damage as well as the formation of Ga1−*<sup>x</sup>* Cr*<sup>x</sup>* N in the implanted part of the sample. The lattice constant of (Ga,Cr)N changes due the presence of chromium, implying that the position of the new peak is related to the concentration of chromium in the material. Hence, the introduction of chromium at interstitial and substitutional sites in GaN is expected to cause lattice expansion to produce a new XRD peak on the left side of the GaN peak [59]. The shifting of additional peaks to the right with annealing, presented in **Figure 24**, points to lattice recovery and improvement in the uniformity of GaCrN which may be due to increase in the substitution probability of chromium atoms.

#### *4.2.2. RBS channelling*

Channelling spectra are presented in **Figure 25** for Cr+ implanted GaN sample at dose 3 ×1016 ions cm−2 and subsequently annealed at 800 and 900°C along with the corresponding minimum channelling yield *χ*min. A minimum channelling yield *χ*min was calculated for the maximum at around 1.65 MeV and is related to the random spectrum of the as-implanted sample (upper spectrum). Cr+ implanted GaN sample at dose 3 ×1016 ions cm−2 and annealed at 800 and 900°C showed the recovery of implantation damage. If we compare these results with Co<sup>+</sup> implanted samples at same dose, we observe that there is less recovery of implantation damage by annealing using RTA for Cr<sup>+</sup> implanted samples. This may have been due to shorter annealing time (2 min).

**Figure 25.** RBS/C of as-implanted sample at 3 × 10<sup>16</sup> ions cm–2 and annealed at 800 and 900°C [68].

#### *4.2.3. AGM and SQUID*

Magnetization versus magnetic field (M-H) curves from AGM measurements at room temperature for the sample implanted to a dose of 3 ×10<sup>16</sup> ions cm−2 and annealed at 800 and 900°C are shown in **Figure 26**, where the signal from the sapphire substrate (diamagnetic) was extracted. The magnetic field was applied parallel to the sample plane. At 300 K, a well-defined hysteresis loop was observed, which provides evidence for the presence of ferromagnetic interactions at room temperature. The saturation field was about 4000 Oe and the coercivity *H*<sup>c</sup> was about 100 Oe for the implanted and subsequently annealed samples. These results confirm that the samples were ferromagnetic even at room temperature. Comparison with same dose for Co<sup>+</sup> implanted samples shows that the saturation magnetization *Ms* values are almost the same in all samples.

Similarly, a well-defined hysteresis loop at 5 K from SQUID was also observed for the implanted and subsequently annealed samples at 800 and 900°C, as shown in **Figure 27**. The saturation field is about 4000 Oe and the coercivity *H*<sup>c</sup> is about 175 Oe for implanted and annealed samples. If we compare the results at 5 K with the same dose of Co<sup>+</sup> implanted samples we find that the saturation magnetization *Ms* values are almost similar for the sample annealed at 800°C. But the *Ms* value for Cr<sup>+</sup> implanted sample annealed at 900°C is 10.7 (×10-5 emug–1) while for the Co+ implanted it is about 4.5 (×10–5 emug–1). A higher value of *Ms* for Cr+ implanted GaN epilayer annealed at 900°C suggests that samples implanted with Cr<sup>+</sup> ions may perform better for dilute magnetic semiconductors (DMSs) compared to Co<sup>+</sup> implanted. Also higher values of *Ms* for implanted samples may suggest that 900°C is a suitable annealing temperature for the activation of dopants.

**Figure 26.** M-H loops at 300 K of sample implanted at dose 3 × 10<sup>16</sup> ions cm−2 and annealed [68].

**Figure 25.** RBS/C of as-implanted sample at 3 × 10<sup>16</sup> ions cm–2 and annealed at 800 and 900°C [68].

The shape, position and number of such new peaks were found different as observed in Co<sup>+</sup> implanted GaN epilayers. The new peak in the XRD scans is assigned to implantation-induced

constant of (Ga,Cr)N changes due the presence of chromium, implying that the position of the new peak is related to the concentration of chromium in the material. Hence, the introduction of chromium at interstitial and substitutional sites in GaN is expected to cause lattice expansion to produce a new XRD peak on the left side of the GaN peak [59]. The shifting of additional peaks to the right with annealing, presented in **Figure 24**, points to lattice recovery and improvement in the uniformity of GaCrN which may be due to increase in the substitu-

cm−2 and subsequently annealed at 800 and 900°C along with the corresponding minimum channelling yield *χ*min. A minimum channelling yield *χ*min was calculated for the maximum at around 1.65 MeV and is related to the random spectrum of the as-implanted sample (upper spectrum).

implanted GaN sample at dose 3 ×1016 ions cm−2 and annealed at 800 and 900°C showed the

implanted samples. This may have been due to shorter annealing time (2 min).

same dose, we observe that there is less recovery of implantation damage by annealing using

N in the implanted part of the sample. The lattice

implanted GaN sample at dose 3 ×1016 ions

implanted samples at

Cr*<sup>x</sup>*

damage as well as the formation of Ga1−*<sup>x</sup>*

36 Ion Implantation - Research and Application

tion probability of chromium atoms.

Channelling spectra are presented in **Figure 25** for Cr+

recovery of implantation damage. If we compare these results with Co<sup>+</sup>

*4.2.2. RBS channelling*

Cr+

RTA for Cr<sup>+</sup>

**Figure 27.** M-H loops at 5K of sample implanted at dose 3 × 10<sup>16</sup> ions cm−2 and annealed [68].

**Figure 28** shows magnetization as a function of temperature for Cr<sup>+</sup> implanted GaN at 3 ×1016 ions cm−2, with multiple exchange interactions indicating that its decay cannot be easily fit to classical description of ferromagnetism, again in agreement with current theories concerning DMS systems with low carrier concentrations. The Cr<sup>+</sup> implanted GaN at 3 ×1016 ions cm−2 and annealed at 900°C showed magnetic moment at lower temperatures, retaining magnetization above the measured temperature of 380 K. This observation is consistent with the epitaxial prepared (Ga,Cr)N magnetic properties observed by Hashimoto et al. who have reported *T*<sup>C</sup> higher than 400 K [35]. The value of *Ms* was higher for the sample annealed at 900°C compared to the sample annealed at 800°C. This increase is assumed to be due to the increase in Cr concentration on Ga sites. These observations suggest that annealing at 900°C is suitable for proper activation of Cr in GaN, which is also supported by the observations reported by Hwang et al. [65].

Well-saturated MH loops were observed in all samples (**Figures 26** and **27**) with finite coercivity, eliminating the likelihood of both paramagnetism and superparamagnetism [63]. Analysing hysteresis loops of the implanted samples assists in the investigation of the magnetic properties of the material. Lateral shifting of hysteresis loop was not observed, and this eliminates spin glass behaviour [64]. These observations imply that there was ferromagnetic ordering in implanted samples at room temperature. No extra peaks were observed on the XRD spectra of the implanted samples (**Figures 23**), reducing the contributions of secondary phases (Cr*<sup>x</sup>* N*y* , CrGa, etc.) to the observed ferromagnetism. Along with magnetization as a function of temperature measurements, FC and ZFC measurements were made on a representative sample and the data did not indicate any blocking temperature that

**Figure 28.** FC/ZFC measurements of the sample implanted at 3 × 10<sup>16</sup> ions cm−2 and annealed at 900°C [68].

**Figure 27.** M-H loops at 5K of sample implanted at dose 3 × 10<sup>16</sup> ions cm−2 and annealed [68].

ions cm−2, with multiple exchange interactions indicating that its decay cannot be easily fit to classical description of ferromagnetism, again in agreement with current theories concerning

annealed at 900°C showed magnetic moment at lower temperatures, retaining magnetization above the measured temperature of 380 K. This observation is consistent with the epitaxial prepared (Ga,Cr)N magnetic properties observed by Hashimoto et al. who have reported *T*<sup>C</sup> higher than 400 K [35]. The value of *Ms* was higher for the sample annealed at 900°C compared to the sample annealed at 800°C. This increase is assumed to be due to the increase in Cr concentration on Ga sites. These observations suggest that annealing at 900°C is suitable for proper activation of Cr in GaN, which is also supported by the observations reported by

Well-saturated MH loops were observed in all samples (**Figures 26** and **27**) with finite coercivity, eliminating the likelihood of both paramagnetism and superparamagnetism [63]. Analysing hysteresis loops of the implanted samples assists in the investigation of the magnetic properties of the material. Lateral shifting of hysteresis loop was not observed, and this eliminates spin glass behaviour [64]. These observations imply that there was ferromagnetic ordering in implanted samples at room temperature. No extra peaks were observed on the XRD spectra of the implanted samples (**Figures 23**), reducing the contributions of

zation as a function of temperature measurements, FC and ZFC measurements were made on a representative sample and the data did not indicate any blocking temperature that

, CrGa, etc.) to the observed ferromagnetism. Along with magneti-

implanted GaN at 3 ×1016

implanted GaN at 3 ×1016 ions cm−2 and

**Figure 28** shows magnetization as a function of temperature for Cr<sup>+</sup>

DMS systems with low carrier concentrations. The Cr<sup>+</sup>

Hwang et al. [65].

38 Ion Implantation - Research and Application

secondary phases (Cr*<sup>x</sup>*

N*y*

can be associated with superparamagnetic behaviour arising from undetected magnetic secondary phase clusters. **Figure 29** presents FC-ZFC measurements for Co<sup>+</sup> and Cr+ ions implanted with the same dose and annealed at 900°C, which also suggests that Cr<sup>+</sup> ions are much suitable for the fabrication of dilute magnetic semiconductors (DMS).

**Figure 29.** FC-ZFC of Co+ and Cr+ implanted samples at 3 × 10<sup>16</sup> ions cm−2 and annealed at 900°C.
