**Effectiveness of DFL composed of SLSs**

PL measurement was applied through a 635-nm solid-state laser excitation at room temperature. The PL results of InAs QDs with different InxGa1-xAs/GaAs DFL parameters are summarized in **Table 2** and shown in **Figure 14**. In view of the PL intensity and the full width at half maximum (FWHM), it can be known that sample 1 (18% In composition) exhibits a higher PL intensity than sample 2(16% In composition) and sample 3(20% In composition). The PL intensity is highly related to the crystal quality, which corresponds to the TDD. Thus, 18% In composition is proved to contribute to the best crystal quality compared with the other indium compositions. When the thickness of GaAs layer was changed, sample 4 is similar to

sample 1 in view of the PL intensity, while sample 5 has a significant reduce. In addition, the FWHM of sample 5 is much wider than other 2. This phenomenon is explained through an 8 nm thin GaAs layer cannot release the strain completely so

*PL spectra of different samples at room temperature. (a) Sample 1, 2, and 3 with indium composition of 18%, 16%, 20% respectively. (b) Sample 1, 4, and 5 with GaAs spacer layer thickness of 10 nm, 9 nm and 8 nm*

*GaAs Compounds Heteroepitaxy on Silicon for Opto and Nano Electronic Applications*

To further investigate the effectiveness of DFL, Cross-sectional TEM measurements were applied to examine the crystal quality and the effectiveness of DFL. The dark-field TEM image and the bright-field TEM image are shown in **Figure 15**. As shown in **Figure 15a**, high number of TDs appear at the GaAs/Si interface propagating towards the epilayers, as most of them annihilate with others in the first 200 nm. However, there are still a great number of TDs propagating towards the upper layer. After the DFL, only a few TDs puncture the DFL and keep propagating

In order to further investigate the DFL performance, DFL efficiency (η) is defined as the fraction of TDs it removes, which can be described as [28, 44].

*<sup>η</sup>* <sup>¼</sup> <sup>1</sup> � *<sup>n</sup>*ð Þ experiment

*The cross-sectional TEM image for TDs around DFL structure. (a) Dark-field TEM image (b) Bright-field*

*n*ð Þ predict

that the accumulated strain degrades the material quality [32].

upwards, while most TDs are blocked by the DFL.

**Figure 14.**

**Figure 15.**

**141**

*TEM image (Reproduced from Ref. [32]).*

*respectively. (Reproduced from Ref. [32]).*

*DOI: http://dx.doi.org/10.5772/intechopen.94609*

## **Figure 13.**

*Schematic diagram of InAs/GaAs DWELL structure monolithically grown on Si substrates with different DFL structures. (a) Schematic diagram of the whole structure. (b) Schematic diagram of the InGaAs/GaAs SLSs as DFL.*


#### **Table 2.**

*Details parameters for InxGa1-xAs/GaAs SLSs in each sample.*

*GaAs Compounds Heteroepitaxy on Silicon for Opto and Nano Electronic Applications DOI: http://dx.doi.org/10.5772/intechopen.94609*

**Figure 14.**

thickness of strained layer, and the repetition of SLSs as well as the DFLs are of the

We have investigated the InxGa1-xAs/GaAs SLSs DFLs [32, 41]. As shown in **Figure 13a**,a1 μm two-step grown GaAs were grown on n-doped Si substrate (001) with 4° offcut towards <011> by using Molecular Beam Epitaxy (MBE) system, while the Si substrate was performed at 900°C for 30 minutes to deoxidize. Then three sets of DFLs were grown, while each DFL structure was composed of five periods of InxGa1-xAs/GaAs SLSs. On the top of DFL, an optimized InAs dot-in-awell (DWELL) structure was embedded between two 100 nm GaAs layers and 50 nm Al0.4Ga0.6As layers [42, 43]. A final 300 nm GaAs was deposited on the

PL measurement was applied through a 635-nm solid-state laser excitation at room temperature. The PL results of InAs QDs with different InxGa1-xAs/GaAs DFL parameters are summarized in **Table 2** and shown in **Figure 14**. In view of the PL intensity and the full width at half maximum (FWHM), it can be known that sample 1 (18% In composition) exhibits a higher PL intensity than sample 2(16% In composition) and sample 3(20% In composition). The PL intensity is highly related to the crystal quality, which corresponds to the TDD. Thus, 18% In composition is proved to contribute to the best crystal quality compared with the other indium compositions. When the thickness of GaAs layer was changed, sample 4 is similar to

*Schematic diagram of InAs/GaAs DWELL structure monolithically grown on Si substrates with different DFL structures. (a) Schematic diagram of the whole structure. (b) Schematic diagram of the InGaAs/GaAs SLSs as*

**Sample InxGa1-xAs GaAs Thickness (nm) PL intensity (a.u) FWHM (nm)** *x* ¼ 0*:*18 10 4 40.3 *x* ¼ 0*:*16 10 2.6 39.8 *x* ¼ 0*:*20 10 2.2 42 *x* ¼ 0*:*18 9 3.9 40.4 *x* ¼ 0*:*18 8 2 46.1

greatest interest and need to be considered when optimizing the SLS.

**Experiment Techniques**

*Post-Transition Metals*

**Effectiveness of DFL composed of SLSs**

whole structure.

**Figure 13.**

*DFL.*

**Table 2.**

**140**

*Details parameters for InxGa1-xAs/GaAs SLSs in each sample.*

*PL spectra of different samples at room temperature. (a) Sample 1, 2, and 3 with indium composition of 18%, 16%, 20% respectively. (b) Sample 1, 4, and 5 with GaAs spacer layer thickness of 10 nm, 9 nm and 8 nm respectively. (Reproduced from Ref. [32]).*

sample 1 in view of the PL intensity, while sample 5 has a significant reduce. In addition, the FWHM of sample 5 is much wider than other 2. This phenomenon is explained through an 8 nm thin GaAs layer cannot release the strain completely so that the accumulated strain degrades the material quality [32].

To further investigate the effectiveness of DFL, Cross-sectional TEM measurements were applied to examine the crystal quality and the effectiveness of DFL. The dark-field TEM image and the bright-field TEM image are shown in **Figure 15**. As shown in **Figure 15a**, high number of TDs appear at the GaAs/Si interface propagating towards the epilayers, as most of them annihilate with others in the first 200 nm. However, there are still a great number of TDs propagating towards the upper layer. After the DFL, only a few TDs puncture the DFL and keep propagating upwards, while most TDs are blocked by the DFL.

In order to further investigate the DFL performance, DFL efficiency (η) is defined as the fraction of TDs it removes, which can be described as [28, 44].

$$\eta = 1 - \frac{n(\text{experiment})}{n(\text{predict})}$$

#### **Figure 15.**

*The cross-sectional TEM image for TDs around DFL structure. (a) Dark-field TEM image (b) Bright-field TEM image (Reproduced from Ref. [32]).*

Where n(experiment) denotes the number of dislocations just above the DFL, and n(predict) denotes the dislocations predicted by the equation n(x) = D0hm, where m = �0.5. The efficiencies of different types of DFL are shown in **Figure 16**. From the figure, it can be known that almost half of TDs propagate through the first set of DFL regardless of indium composition of InxGa1-xAs layer. However, the sample with In0.18Ga0.82As/GaAs SLSs shows a superior ability in filtering efficiency compared to others, which achieves over 80%. The demonstrated highest efficiency presents a good balance between TD generation and strain induced to annihilate TDs.

**Theoretical models.**

*DOI: http://dx.doi.org/10.5772/intechopen.94609*

Δ*Edis <sup>L</sup>* <sup>¼</sup> <sup>1</sup> 2*π*

**Experiment Techniques**

mated to be (2–5) � 107 cm�<sup>2</sup>

Unit (cm�<sup>2</sup>

**Effectiveness of DFL composed of QDs**

**Quantum Dots Dot Density QD base area Bending area ratio**

) In0.6Al0.4As <sup>2</sup> � <sup>10</sup><sup>11</sup> <sup>27</sup>–<sup>56</sup> �<sup>0</sup> �<sup>0</sup> In0.5Ga0.5As <sup>5</sup> � 1010 <sup>80</sup>–<sup>132</sup> <sup>&</sup>lt;1% �<sup>0</sup> InAs <sup>2</sup> � <sup>10</sup><sup>10</sup> <sup>120</sup>–<sup>210</sup> 80% 10%

) (nm<sup>2</sup>

*Bending area ratios for different QDs (Reproduced from Ref. [48]).*

is grown.

**Table 3.**

**143**

calculated through

Several parameters need to be considered when using self-organized QDs as DFLs including QD composition, size, areal density, and the number of dots. The theoretical simulation of the effectiveness of dislocation bending is developed by J. Yang et al. [48], which assuming QD islands are coherently strained with pyramidal in shape. The energy ΔErel releases when the MD formed to bend the TDs can be

*GaAs Compounds Heteroepitaxy on Silicon for Opto and Nano Electronic Applications*

*<sup>L</sup>* <sup>¼</sup> <sup>2</sup>*Gdot*ð Þ <sup>1</sup> <sup>þ</sup> *<sup>ν</sup>*

ð Þ <sup>1</sup> � *<sup>ν</sup> feff beff <sup>h</sup>*

*<sup>b</sup>*<sup>2</sup> <sup>1</sup> � *<sup>ν</sup> cos* <sup>2</sup>*<sup>β</sup>* 1 � *ν*

The bending will occur when the ΔErel ≥ ΔEdis. Here, L is the length of the MD, Gdot (Gbuff) is the shear module of dot (buffer layer), ν is the Poisson ration,b is the Burger's vector, beff is the project of Burger's vector on the buffer layer, feff is the effective lattice mismatch between the QD and the underlying buffer layer, h is the height of QD, β is the angle between the Burger's vector and the dislocation line, r

According to the simulations, the bending area ratio, which denotes the bending area divided by the area of QD bases, is shown in **Table 3**. InAs QDs are proved to be the most suitable self-organized QD serving as dislocation filters with the largest

Considering the theory and results above, InAs QDs DFL has the highest efficiency compared with other QD DFLs for GaAs monolithically grown on Si. In order to investigate the TD behavior in QD DFL region, a buffer structure shown in **Figure 17** is grown with N-type doped InAs QD dislocation filter on Si (001) substrate with 4° misorientation towards [111]. A thin (<2 μm) GaAs layer is first grown by MOVPE with free of antiphase domain. The TDD at its surface is esti-

separated by 50 nm GaAs layers. On the top of QD dislocation filter, a 800 nm GaAs

Cross-sectional TEM measurements were applied to investigate the propagation of dislocations in the QD DFLs. Images were obtained with various g, including [2,2,0], [1,1,1], and [0,0,4] as shown in **Figure 18a, b** and **c**, respectively. Two different types of TDs can be observed: pure edge dislocation labeled as C and 60° mixed TDs labeled as A and B. It is obvious from the cross-sectional TEM images

ln <sup>2</sup>*<sup>r</sup>*

*b* 

. The dislocation filter consists of 10 layers of InAs QD

**of a single QD**

**Bending area ratio of a single layer**

þ 1

Δ*Erel*

While the dislocation self-energy ΔEdis can be described as

*GbuffGdot Gbuff* þ *Gdot*

denotes an outer cutoff radius of the dislocation strain field.

bending area and largest critical layer numbers for QD multilayers [48].

Apart from the InGaAs/GaAs SLSs, InAlAs/GaAs SLSs is also another great option severing as DFL [45–47]. Due to the larger shear modulus of InAlAs, it is expected that the critical misfit for generating new TDs is much larger than that of InGaAs. We compared In0.15Ga0.85As/GaAs DFL and In0.15Al0.85As/GaAs DFL by growing InAs/GaAs QD samples on Si (100) substrates [41]. The In0.15Ga0.85As/ GaAs DFL composed three repeats of 5 period of 10-nm In0.15Al0.85As and 10-nm GaAs SLS separated by 400 nm GaAs spacer layer, while the In0.15Al0.85As/GaAs DFL had almost same structure except replacing the In0.15Ga0.85As to In0.15Al0.85As. EPD were counted for both samples. After three sets of SLSs, the defects density of the sample with InAlAs/GaAs DFL was around 2 � <sup>10</sup><sup>6</sup> cm�<sup>2</sup> , while the other one with InGaAs/GaAs DFL was round 5 � <sup>10</sup><sup>6</sup> cm�<sup>2</sup> [41]. In addition, the sample with InAlAs/GaAs DFL had a higher PL peak intensity as well as thermal activation energy compared to the sample with InGaAs/GaAs [41].
