**5.1. Radiation-induced recombination centers in Si**

In order to clarify the origins of radiation-induced defects in Si and correlation between their behavior and Si solar cell properties, DLTS analysis has been carried out. DLTS measurements were made using a quiescent bias of -2V and a saturating fill pulse of 2V, 1 ms duration. Figure. 4 shows both the majority- and minority-carrier DLTS spectra of some of the same Si diode as a function of 1 MeV electron fluence. A large concentration of a minority carrier trap with an activation energy of about EC-0.18 eV has been observed, as well as the majority carrier traps at around Ev+0.18eV and Ev+0.36eV.

A comparison of the total majority carrier defect concentration observed by DLTS with the measured change in carrier concentration for all the diodes is made in Figure 5. The compen‐ sation observed in the C-V profile is mainly caused by the minority carrier trap EC-0.18 eV shown in Figure 4. The total concentrations of these majority-carrier traps and the minoritycarrier trap at around Ec-0.18eV have been found to be nearly equal to the change in carrier concentrations. The concentration of the minority carrier trap at around Ec-0.18eV, was high enough to be responsible for most of the observed compensation and subsequently type conversion of the base layer from p to n-type. The Ev+0.36eV defect is thought to be responsible for minority-carrier lifetime (diffusion length) deg radiation according to the annealing experiments in the higher temperature range as will be described below. This means that the Ev+0.36eV is thought to act as a recombination center, in addition to a role as a majority-carrier trap center.

Figure. 4. DLTS spectra of p-type Si before and after 1 MeV electron irradiation: (d) before irradiation, (b) and (a) majority and minority carrier signals after 1 x 10<sup>16</sup> cm-2 fluence, respectively and (c) majority carrier signal after 1 x 10<sup>17</sup> cm-2 fluence. The base of the diode irradiated with 1 x 10<sup>17</sup>cm-2 electrons was n-type and required a **Figure 4.** DLTS spectra of p-type Si before and after 1 MeV electron irradiation: (d) before irradiation, (b) and (a) ma‐ jority and minority carrier signals after 1 x 1016 cm-2 fluence, respectively and (c) majority carrier signal after 1 x 1017 cm-2 fluence. The base of the diode irradiated with 1 x 1017 cm-2 electrons was n-type and required a correction to the spectrum to account for the effects of series resistance.

correction to the spectrum to account for the effects of series resistance.

Comment [A1]: may be mention to 0.71 will be

Comment [A2]: no need to add rc equation

Comment [B3R2]:

Comment [B4R2]:

Comment [B5R2]:

necessary

**Figure 5.** Total trap concentration observed by DLTS in comparison with the change in carrier concentration observed by C-V measurements at 300 K as a function of 1 MeV electron fluence.[15]

thought to be responsible for minority-carrier lifetime (diffusion length) deg radiation according to the annealing experiments in the higher temperature range as will be described below. This means that the Ev+0.36eV is thought to act as a

Figure 5. Total trap concentration observed by DLTS in comparison with the change in carrier concentration observed by

tially, the observed concentration of the Ev+0.36eV defects had increased as shown in the Figure 6 . This suggests that

It is important to note that after annealing at 250°C, although the carrier concentration had recovered substan-

recombination center, in addition to a role as a majority-carrier trap center.

C-V measurements at 300 K as a function of 1 MeV electron fluence.[15]

the Ev+0.36eV defects are not principally responsible for carrier removal.

(d )

observed compensation and subsequently type conversion of the base layer from p to n-type. The Ev+0.36eV defect is

correction to the spectrum to account for the effects of series resistance.

by C-V measurements at 300 K as a function of 1 MeV electron fluence.[15]

spectrum to account for the effects of series resistance.

212 Solar Cells - New Approaches and Reviews

Figure. 4. DLTS spectra of p-type Si before and after 1 MeV electron irradiation: (d) before irradiation, (b) and (a) majority and minority carrier signals after 1 x 10<sup>16</sup> cm-2 fluence, respectively and (c) majority carrier signal after 1 x 10<sup>17</sup> cm-2 fluence. The base of the diode irradiated with 1 x 10<sup>17</sup>cm-2 electrons was n-type and required a

**Figure 4.** DLTS spectra of p-type Si before and after 1 MeV electron irradiation: (d) before irradiation, (b) and (a) ma‐ jority and minority carrier signals after 1 x 1016 cm-2 fluence, respectively and (c) majority carrier signal after 1 x 1017 cm-2 fluence. The base of the diode irradiated with 1 x 1017 cm-2 electrons was n-type and required a correction to the

thought to be responsible for minority-carrier lifetime (diffusion length) deg radiation according to the annealing experiments in the higher temperature range as will be described below. This means that the Ev+0.36eV is thought to act as a

Figure 5. Total trap concentration observed by DLTS in comparison with the change in carrier concentration observed by

**Figure 5.** Total trap concentration observed by DLTS in comparison with the change in carrier concentration observed

tially, the observed concentration of the Ev+0.36eV defects had increased as shown in the Figure 6 . This suggests that

It is important to note that after annealing at 250°C, although the carrier concentration had recovered substan-

recombination center, in addition to a role as a majority-carrier trap center.

C-V measurements at 300 K as a function of 1 MeV electron fluence.[15]

the Ev+0.36eV defects are not principally responsible for carrier removal.

Figure 6. Comparison of isochronal annealing of densities of Ec-0.18eV, Ev+0.18eV and Ev+0.36eV defect centers measured by DLTS with that of carrier concentration of p-type Si irradiated with 1-MeV electrons. Each annealing step duration was 20 min.[15]. **Figure 6.** Comparison of isochronal annealing of densities of Ec-0.18eV, Ev+0.18eV and Ev+0.36eV defect centers meas‐ ured by DLTS with that of carrier concentration of p-type Si irradiated with 1-MeV electrons. Each annealing step du‐ ration was 20 min.[15].

It is important to note that after annealing at 250°C, although the carrier concentration had recovered substantially, the observed concentration of the Ev+0.36eV defects had increased as shown in the Figure 6 . This suggests that the Ev+0.36eV defects are not principally responsible for carrier removal. We were able to confirm that the degradation of lifetime (diffusion length) is likely to be caused by the introduction of It is important to note that after annealing at 250°C, although the carrier concentration had recovered substantially, the observed concentration of the Ev+0.36eV defects had increased as shown in the Figure 6. This suggests that the Ev+0.36eV defects are not principally responsible for carrier removal.

the minority-carrier trap at around Ec-0.18eV have been found to be nearly equal to the change in carrier concentrations. The concentration of the minority carrier trap at around Ec-0.18eV, was high enough to be responsible for most of the Comment [A1]: may be mention to 0.71 will be dominant hole level Ev+0.36eV and annealing behavior of this level govern the diffusion length recovery [15]. Figure 7 compares isochronal annealing of density of the majority-carrier trap at Ev+0.36eV measured by DLTS and that of recombination center determined by solar cell properties in p-type Si irradiated with 1-MeV electrons. Changes in the relative recombination center density Nr with annealing were also estimated by changes in short-circuit current density Jsc of the solar cell according to the following equation: 2 2 2 2 0 2 2 1/ 1/ (1/ ) <sup>~</sup> 1/ 1/ 1/ 1/ (1/ ) *sca sco a a sca ra J J J L L L N* (28) We were able to confirm that the degradation of lifetime (diffusion length) is likely to be caused by the introduction of dominant hole level Ev+0.36eV and annealing behavior of this level govern the diffusion length recovery [15]. Figure 7 compares isochronal annealing of density of the majority-carrier trap at Ev+0.36eV measured by DLTS and that of recombination center determined by solar cell properties in p-type Si irradiated with 1-MeV electrons. Changes in the relative recombination center density Nr with annealing were also estimated by changes in short-circuit current density Jsc of the solar cell according to the following equation:

2

*sc*

(1/ )

*J*

2 0

2

*L L*

2

(1/ )

*L*

*r*

*N*

$$\frac{N\_{su}}{N\_{sp}} = \frac{\Delta(1/L\_{s}^{2})}{\Delta(1/L\_{\rho}^{2})} = \frac{\left[1/L\_{s}^{2} - 1/L\_{0}^{2}\right]}{\left[1/L\_{\rho}^{2} - 1/L\_{0}^{2}\right]} \sim \frac{\Delta(1/f\_{su}^{2})}{\Delta(1/f\_{su}^{2})} = \frac{\left[1/f\_{su}^{2} - 1/f\_{su}^{2}\right]}{\left[1/f\_{su}^{2} - 1/f\_{su}^{2}\right]}\tag{28}$$

<sup>2</sup> <sup>2</sup>

*J J*

*sc sco*

ties. This implies that the Ev+0.36eV majority-carrier trap center may also act as a recombination center.

1/ 1/

1.4 1.6 Recombination Center (Solar Cell Property) Features of the Ev+0.36eV majority-carrier trap center with reverse annealing stage at 2000 C~3000 C and a recovery stage at around 3500 C are similar to the changes in minority-carrier diffusion length L determined from the solar cell properties. This implies that the Ev+0.36eV majority-carrier trap center may also act as a recombination center.

0.8 1.0 1.2 EV + 0.36 eV (DLTS) Remaining factor As shown in Figure 6 the estimated initial concentration of the trap at approximately EC-0.18eV is about 60% of the change in carrier concentration and therefore populous enough to be the dominating influence. Furthermore, the recovery of the carrier concentration after annealing occurs over roughly the same temperature range as disappearance of the minority trap signal.

C)

0 100 200 300 400

Annealing temperature (<sup>o</sup>

Comment [A2]: no need to add rc equation

Comment [B3R2]:

0.0 0.2 0.4 0.6

1-MeV electron

Comment [B4R2]:

Comment [B5R2]:

*r ra*

*N N*

**Figure 7.** Comparison of isochronal annealing of the majority-carrier trap at Ev+0.36eV measured by DLTS with that of the dominant recombination center determined by solar cell properties in p-type Si irradiated with 1-MeV electrons [15].

This evidence is, therefore, coherent with the hypothesis that the Ec-0.18 eV center is mainly responsible for the compensation of the base layer. The radiation-induced traps, which play an important role regarding the carrier removal and conduction type conversion of the base region, should be principally deep-level donors, which must be positively charged before electron capture.

$$X^\* + e^- \leftrightarrow X^0 \tag{29}$$

0 100 200 300 400

C)

Figure 6. Comparison of isochronal annealing of densities of Ec-0.18eV, Ev+0.18eV and Ev+0.36eV defect centers measured by DLTS with

It is important to note that after annealing at 250°C, although the carrier concentration had recovered substantially, the observed concentration of the Ev+0.36eV defects had increased as shown in the Figure 6 . This suggests that the Ev+0.36eV

We were able to confirm that the degradation of lifetime (diffusion length) is likely to be caused by the introduction of dominant hole level Ev+0.36eV and annealing behavior of this level govern the diffusion length recovery [15]. Figure 7 compares isochronal annealing of density of the majority-carrier trap at Ev+0.36eV measured by DLTS and that of recombination center determined by solar cell properties in p-type Si irradiated with 1-MeV electrons. Changes in the relative recombination center density Nr with annealing were also estimated by changes in short-circuit current density Jsc of the

Features of the Ev+0.36eV majority-carrier trap center with reverse annealing stage at 2000 C~3000 C and a recovery stage at around 3500 C are similar to the changes in minority-carrier diffusion length L determined from the solar cell proper-

that of carrier concentration of p-type Si irradiated with 1-MeV electrons. Each annealing step duration was 20 min.[15].

Annealing temperature (<sup>o</sup>

defects are not principally responsible for carrier removal.

(1/ )

*J J* 2 2

*sc*

  <sup>2</sup> <sup>2</sup> 2 2

*J J J J*

*sc sco sca sco*

(28)

1/ 1/ 1/ 1/

solar cell according to the following equation:

2 0

(1/ ) <sup>~</sup> 1/ 1/

2 0

*a a sca*

*L L L L*

2

2 2

(1/ ) (1/ )

*L L* 2

1/ 1/

(P0 -Pa )/((P0 -P )

1.0 1-M eV electron

E <sup>C</sup>- 0.18 eV

EV + 0.36 eV

EV + 0.18 eV

0.0

0.2

0.4

0.6

Remaining factor

0.8

## **5.2. Role of boron on compensator center**

Interestingly, the introduction rate of the EC-0.18eV electron level in B-doped samples is strongly boron concentration dependent. Comparison of introduction behavior, annealing kinetics and the strong relation to boron and oxygen contents, supports correlation of this level (EC-0.18eV) with the Bi -Oi (Figure 8).

### **5.3. Role of gallium on compensator center**

One of the most interesting and technological important feature of our work was the disap‐ pearance of the dominant donor like electron level EC-0.18 eV in Ga-doped CZ- grown samples [17] (Figure 9). As we have discussed above this level acts as a compensator center, which is positive charge before electron capture. The concentration of this level is about 60% of the change in carrier concentration after heavy fluences and therefore populous enough to be the dominating influence on device performance. This implies that carrier removal effects can be

ties. This implies that the Ev+0.36eV majority-carrier trap center may also act as a recombination center. tents, supports correlation of this level (EC-0.18eV) with the Bi-Oi (Figure 8). Deep Level Transient Spectroscopy: A Powerful Experimental Technique for Understanding the Physics… http://dx.doi.org/10.5772/59419 215

Figure 7. Comparison of isochronal annealing of the majority-carrier trap at Ev+0.36eV measured by DLTS with that of the dominant

As shown in Figure 6 the estimated initial concentration of the trap at approximately EC-0.18eV is about 60% of the change in carrier concentration and therefore populous enough to be the dominating influence. Furthermore, the recovery of the carrier concentration after annealing occurs over roughly the same temperature range as disappearance of the minority trap signal. This evidence is, therefore, coherent with the hypothesis that the Ec-0.18 eV center is mainly responsible for the compensation of the base layer. The radiation-induced traps, which play an important role regarding the carrier removal and conduction type conversion of the base region, should be principally deep-level donors, which must

Interestingly, the introduction rate of the EC-0.18eV electron level in B-doped samples is strongly boron concentration dependent. Comparison of introduction behavior, annealing kinetics and the strong relation to boron and oxygen con-

Figure 8. Introduction rates of the interstitial related defects in 10 MeV proton irradiated p-Si as a function of background impurity con-

recombination center determined by solar cell properties in p-type Si irradiated with 1-MeV electrons [15].

1 0 1 5 1 0 1 6 1 0 1 7 0.01

*Xe X* <sup>0</sup>

Boron concentration (cm -3 )

O i

B i -B <sup>s</sup> (0.30 eV)

 ~ 9 x 10 1 7 cm -3 C ~ 5 x 10 1 5 cm -3

**5.2. Role of boron on compensator center**

10 M eV proton = 3 x 10 1 3 cm -2

(29)

be positively charged before electron capture.

0.1

[18-20] complex.

1

C i -O <sup>i</sup> (0.36 eV)

B i -O <sup>i</sup> (0.18 eV)

Introduction rate (cm-1

)

1 0

100

**5.3 Role of Gallium on Compensator Center** One of the most interesting and technological important feature of our work was the disappearance of the dominant **Figure 8.** Introduction rates of the interstitial related defects in 10 MeV proton irradiated p-Si as a function of back‐ ground impurity concentration [16].

donor like electron level EC-0.18 eV in Ga-doped CZ- grown samples [17] (Figure 9). As we have discussed above this

instead of boron. The absence of this level in Ga-doped Si gives support that this center in B-doped Si is related to Bi


partially offset by using Ga as dopant instead of boron. The absence of this level in Ga-doped Si gives support that this center in B-doped Si is related to Bi -Oi [18-20] complex. level acts as a compensator center, which is positive charge before electron capture. The concentration of this level is about 60% of the change in carrier concentration after heavy fluences and therefore populous enough to be the dominating influence on device performance. This implies that carrier removal effects can be partially offset by using Ga as dopant centration [16].

**Figure 9.** Comparison of the minority carrier DLTS spectra measured for boron-or gallium –doped CZ-grown Si irradi‐ ated with 1-MeV 3 x 1016 electrons/cm2 . The spectra were acquired using a reverse bias of 2 V, a pulse voltage of -1.5V, a pulse width of 1x 10-3 s and period width of 200 ms. [17].

### **5.4. Superior radiation resistance of InGaP solar cells**

This evidence is, therefore, coherent with the hypothesis that the Ec-0.18 eV center is mainly responsible for the compensation of the base layer. The radiation-induced traps, which play an important role regarding the carrier removal and conduction type conversion of the base region, should be principally deep-level donors, which must be positively charged before

**Figure 7.** Comparison of isochronal annealing of the majority-carrier trap at Ev+0.36eV measured by DLTS with that of the dominant recombination center determined by solar cell properties in p-type Si irradiated with 1-MeV electrons

0 100 200 300 400

Annealing temperature (<sup>o</sup>

EV + 0.36 eV (DLTS)

Interestingly, the introduction rate of the EC-0.18eV electron level in B-doped samples is strongly boron concentration dependent. Comparison of introduction behavior, annealing kinetics and the strong relation to boron and oxygen contents, supports correlation of this level

One of the most interesting and technological important feature of our work was the disap‐ pearance of the dominant donor like electron level EC-0.18 eV in Ga-doped CZ- grown samples [17] (Figure 9). As we have discussed above this level acts as a compensator center, which is positive charge before electron capture. The concentration of this level is about 60% of the change in carrier concentration after heavy fluences and therefore populous enough to be the dominating influence on device performance. This implies that carrier removal effects can be

<sup>0</sup> *Xe X* + - + « (29)

C)

0 100 200 300 400

C)

Figure 6. Comparison of isochronal annealing of densities of Ec-0.18eV, Ev+0.18eV and Ev+0.36eV defect centers measured by DLTS with

It is important to note that after annealing at 250°C, although the carrier concentration had recovered substantially, the observed concentration of the Ev+0.36eV defects had increased as shown in the Figure 6 . This suggests that the Ev+0.36eV

We were able to confirm that the degradation of lifetime (diffusion length) is likely to be caused by the introduction of dominant hole level Ev+0.36eV and annealing behavior of this level govern the diffusion length recovery [15]. Figure 7 compares isochronal annealing of density of the majority-carrier trap at Ev+0.36eV measured by DLTS and that of recombination center determined by solar cell properties in p-type Si irradiated with 1-MeV electrons. Changes in the relative recombination center density Nr with annealing were also estimated by changes in short-circuit current density Jsc of the

Features of the Ev+0.36eV majority-carrier trap center with reverse annealing stage at 2000 C~3000 C and a recovery stage at around 3500 C are similar to the changes in minority-carrier diffusion length L determined from the solar cell proper-

that of carrier concentration of p-type Si irradiated with 1-MeV electrons. Each annealing step duration was 20 min.[15].

Annealing temperature (<sup>o</sup>

defects are not principally responsible for carrier removal.

(1/ )

*J J* 2 2

*sc*

  <sup>2</sup> <sup>2</sup> 2 2

*J J J J*

*sc sco sca sco*

(28)

1/ 1/ 1/ 1/

solar cell according to the following equation:

2 0

(1/ ) <sup>~</sup> 1/ 1/

2 0

*a a sca*

*L L L L*

2

2 2

(1/ ) (1/ )

*L L*

*r ra*

*N N*

214 Solar Cells - New Approaches and Reviews

2

1/ 1/

(P0 -Pa )/((P0 -P )

1.0 1-M eV electron

E <sup>C</sup>- 0.18 eV

EV + 0.36 eV

EV + 0.18 eV

0.0

0.2

0.4

0.6

Remaining factor

0.8

electron capture.

[15].

(EC-0.18eV) with the Bi

**5.2. Role of boron on compensator center**

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Remaining factor

1-MeV electron

Recombination Center (Solar Cell Property)


**5.3. Role of gallium on compensator center**

(Figure 8).

In this section, we present the direct observation of minority-carrier injection annealing of the dominant 1 MeV electron irradiation-induced hole trap labeled H2 located at 0.50-0.55 eV tively slowly

5.3 Superior Radiation Resistance of InGaP Solar Cells

above the valence band in p-InGaP by Deep Level Transient Spectroscopy (DLTS). Further‐ more, an evidence of a large minority carrier capture cross section for this hole trap has been obtained by double-carrier pulse DLTS which demonstrate the important role of this trap as an recombination center. The one aim of present study was to clarify the mechanism involved in minority-carrier injection-enhanced annealing of the radiation-induced defect H2 in p-InGaP [22-27]. In this section, we present the direct observation of minority-carrier injection annealing of the dominant 1 MeV electron irradiation-induced hole trap labeled H2 located at 0.50-0.55 eV above the valence band in p-InGaP by Deep Level Transient Spectroscopy (DLTS). Furthermore, an evidence of a large minority carrier capture cross section for this hole trap has been obtained by double-carrier pulse DLTS which demonstrate the important role of this trap as an recombination center. The one aim of present study was to clarify the mechanism involved in minority-carrier injectionenhanced annealing of the radiation-induced defect H2 in p-InGaP [22-27].

density of 0.1 A cm-2 [21]. **Figure 10.** Changes of the DLTS spectrum of trap H2 with various time of injection at 25o C with an injection density of 0.1 A cm-2 [21].

C with an injection

Figure 10. Changes of the DLTS spectrum of trap H2 with various time of injection at 25<sup>o</sup>

10-7

InGaP, determined from solar cells property ( Jsc or L) and for H2 trap observed by DLTS [21].

10-6

10-5

10-4

The important result of this study is the influence of minority-carrier injection on the annealing kinetics of dominant hole level H2 [21]. In order to clarify the recovery of the solar cells properties following minority-carrier injection annealing, we carried out a systematic study of the variation of the concentration of the hole level H2 using a constant amplitude of forward bias injection (0.1 A/cm<sup>2</sup> ) at various temperatures for 0.5, 1, 2, 5, 10 and 20 min. The majority-carrier emission DLTS scans taken after different forward bias injection steps show a pronounced reduction in the H2 amplitude as shown in Figure. 10, which is correlated with a recovery of the maximum power output of the solar cells. It should be noted that the H2 peak; is rather broad and after pronounced reduction following forward bias, exhibits a double structure, indicating that this peak consists of more than one closely spaced peaks; one on the high temperature side appear to anneal rela-Figure 11 presents the temperature dependence of the annealing rate A\* of the hole trap H2 by minority-carrier injection-enhanced processes, determined from DLTS. The important result of this study is the influence of minority-carrier injection on the annealing kinetics of dominant hole level H2 [21]. In order to clarify the recovery of the solar cells properties following minority-carrier injection annealing, we carried out a systematic study of the variation of the concentration of the hole level H2 using a constant amplitude of forward bias injection (0.1 A/cm2 ) at various temperatures for 0.5, 1, 2, 5, 10 and 20 min. The majoritycarrier emission DLTS scans taken after different forward bias injection steps show a pro‐ nounced reduction in the H2 amplitude as shown in Figure. 10, which is correlated with a recovery of the maximum power output of the solar cells. It should be noted that the H2 peak; is rather broad and after pronounced reduction following forward bias, exhibits a double structure, indicating that this peak consists of more than one closely spaced peaks; one on the high temperature side appear to anneal relatively slowly

> 10-2 10-1 Injection anneals (∆E = 0.51±0.09 eV) Figure 11 presents the temperature dependence of the annealing rate *A\** of the hole trap H2 by minority-carrier injection-enhanced processes, determined from DLTS.

> 10-3 by DLTS Annealing Rate ( s-1)A comparison is given with the injection-enhanced annealing rates estimated by changes in short-circuit current density *Jsc* of the solar cells according to the following:

> > Thermal anneals (∆E= 1.68± 0.14eV) by DLTS

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

1000/T (K-1) Figure. 11. Temperature dependence of the thermal and injection annealing rates of the radiation-induced defects in p-

Injection anneals (∆E= 0.54±0.11 eV ) by solar cell propetry

) at various temperatures for 0.5, 1, 2, 5, 10 and 20 min. The majority-carrier emission

C with an injection

The important result of this study is the influence of minority-carrier injection on the annealing kinetics of dominant hole level H2 [21]. In order to clarify the recovery of the solar cells properties following minority-carrier injection annealing, we carried out a systematic study of the variation of the concentration of the hole level H2 using a constant amplitude of

Temperature (K)

Figure 10. Changes of the DLTS spectrum of trap H2 with various time of injection at 25<sup>o</sup>

200 250 300 350

DLTS scans taken after different forward bias injection steps show a pronounced reduction in the H2 amplitude as shown in Figure. 10, which is correlated with a recovery of the maximum power output of the solar cells. It should be noted that the H2 peak; is rather broad and after pronounced reduction following forward bias, exhibits a double structure, indicating that this peak consists of more than one closely spaced peaks; one on the high temperature side appear to anneal rela-

 In this section, we present the direct observation of minority-carrier injection annealing of the dominant 1 MeV electron irradiation-induced hole trap labeled H2 located at 0.50-0.55 eV above the valence band in p-InGaP by Deep Level Transient Spectroscopy (DLTS). Furthermore, an evidence of a large minority carrier capture cross section for this hole trap has been obtained by double-carrier pulse DLTS which demonstrate the important role of this trap as an recombination center. The one aim of present study was to clarify the mechanism involved in minority-carrier injection-

0.5 min

p-InGaP emission rate=1005 s-1 0 min

> Injection anneals 100mA/cm<sup>2</sup>

 at 25 <sup>o</sup> C

5 min

20 min

10 min

Figure. 11. Temperature dependence of the thermal and injection annealing rates of the radiation-induced defects in p-InGaP, determined from solar cells property ( Jsc or L) and for H2 trap observed by DLTS [21]. **Figure 11.** Temperature dependence of the thermal and injection annealing rates of the radiation-induced defects in p-InGaP, determined from solar cells property (*Jsc* or *L*) and for H2 trap observed by DLTS [21].

$$\frac{N\_{\rm TI}}{N\_{\rm T\rho}} = \frac{L\_{\rho}^{2} \left(L\_{0}^{2} - L\_{I}^{2}\right)}{\left[L\_{I}^{2} \left(L\_{0}^{2} - L\_{\rho}^{2}\right)\right]} \sim \frac{\int\_{s\rho\rho}^{2} \left(\int\_{s\epsilon 0}^{2} - \int\_{s\epsilon l}^{2}\right)}{\left[\int\_{s\epsilon l}^{2} \left(\int\_{s\mu 0}^{2} - \int\_{s\rho 0}^{2}\right)\right]} \tag{30}$$

where suffixes 0, φ, and I correspond to before and after irradiation, and after injection, respectively. The important result of this study is the direct relationship between the annealing rates, the solar cells properties and the H2 trap.

A close agreement between activation energy for recovery of radiation-induced defects, determined by solar cell properties and for the hole traps H2, demonstrates that this trap controls the minority-carrier lifetime. This result demonstrates that the dominant majority hole level H2 (EV+0.5–0.55 eV) is the recombination center, which governs the minority-carrier lifetime in n+ –p InGaP solar cells.
