Photoreflectance and photoluminescence study of localization effects in GaAsBi alloys

Optical Materials xxx (2015) xxx–xxx

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Photoreflectance and photoluminescence study of localization effects in GaAsBi alloys H. Fitouri ⇑, Y. Essouda, I. Zaied, A. Rebey, B. El Jani University of Monastir, Unité de Recherche sur les Hétéro-Epitaxies et Applications, Faculty of Sciences of Monastir, 5019 Monastir, Tunisia

a r t i c l e

i n f o

Article history: Received 15 May 2014 Received in revised form 14 November 2014 Accepted 1 December 2014 Available online xxxx Keywords: GaAsBi MOVPE Photoreflectance Photoluminescence

a b s t r a c t Photoreflectance (PR) and photoluminescence (PL) spectra of GaAs1xBix alloys grown by metalorganic vapor phase epitaxy, for x up to 4.8%, were measured at temperatures ranging from 12 to 300 K. The PR signal shifts due to the temperature change decreases with increasing Bi content of GaAsBi alloys. For temperature below 100 K, a dominant peak in PL spectra of GaAsBi was observed. This peak is attributed to carrier localization resulting from Bi-related localized states in GaAsBi. A decrease in PR signal has been also found when the temperature was lowered. This behavior is attributed to a weakening of modulation efficiency, which is induced by carrier localization that has been evidenced in low temperature PL. The localized state emission partly contributes to the decrease in the band gap energy shift. In addition, at high temperatures the small PR signal shift is due to the reduction in the temperature dependence of the band gap energy. The analysis of the band gap energy evolution with temperature using the Bose– Einstein statistical expression shows that the average phonon energy is much larger than that expected from the linear interpolation between GaAs and GaBi. This fact is related to the interaction between electrons and phonons localized at Bi atoms playing an important role in the reduction of the temperature dependence of the band gap energy of GaAsBi alloys. Ó 2015 Elsevier B.V. All rights reserved.

1. Introduction Currently there is a considerable interest in III–V–Bi alloys, such as GaAsBi because of their fundamental physical properties and potential device applications [1–3]. The substitution of a few percent of As by Bi atoms, acting as an isoelectronic impurity, in GaAs leads to a large reduction in band gap energy, accompanied with a rapid increase in the spin–orbit-splitting energy [3–7]. This characteristic makes GaAsBi alloys very attractive candidates for high performance infrared emitters and detectors and high-efficiency solar cells [8–10]. Several theoretical and spectroscopic studies show that only the valence band of GaAs is affected by alloying it with Bi [9,11,12]. The Bi incorporation in GaAs is mainly perturbing the valence band and adding a carrier localization effect. Disorder effects, i.e., compositional fluctuations together with the Bi clustering within the GaAsBi alloy structure, lead to an increasing density of localized states [13–15]. However, the photoluminescence (PL) spectra measured at low temperature are dominated by the recombination of localized carriers trapped at local potential minima [15]. The GaAsBi alloy was successfully grown by metalorganic vapor

phase epitaxy (MOVPE) and molecular beam epitaxy [16–21]. Epitaxial layers of GaAsBi have demonstrated a reduced temperature dependence of the lasing wavelength, which makes them promising for the manufacture of laser diodes and semiconductor optical amplifiers that do not require Peltier cooling [10]. Recently, a large number of reports on detailed optical characterizations of GaAsBi were published [7,14,22–37]. They include temperature dependence of PL, time-resolved PL, Photomodulated transmittance and photoreflectance (PR). These reports are more or less related to the effect of the alloy disorder characteristic of the bismuth containing alloys, which leads to radiative recombination of the localized carriers at low temperature. In view of these reports, many fundamental optical properties of GaAsBi alloys grown by MOVPE are yet unknown. Thus, detailed studies are necessary in order to clarify the role of Bi amount on the optical properties of GaAsBi. In this paper, we report a detailed PR study on the Bi content and temperature dependence to the optical transition in GaAsBi and the influence of localized states. The PR behavior change will be discussed together with PL measurements. 2. Experimental details

⇑ Corresponding author. Tel.: +216 73 500 274; fax: +216 73 500 278. E-mail addresses: hedi.fi[email protected] (H. Fitouri), [email protected] (A. Rebey).

The samples studied in the present work were grown by atmospheric pressure metalorganic vapor phase epitaxy with varying Bi

http://dx.doi.org/10.1016/j.optmat.2014.12.020 0925-3467/Ó 2015 Elsevier B.V. All rights reserved.

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H. Fitouri et al. / Optical Materials xxx (2015) xxx–xxx

contents up to 4.8%. The Bi content and thickness of the GaAsBi epilayers were determined using high resolution X-ray diffraction by assessing the Bragg angle of the GaAsBi reflections and pendellosung oscillations respectively [5]. The growth parameters are summarized in Table 1. The PR measurements were carried out employing a standard setup with the 514.5 nm line of an argon laser as the pump light in a variable temperature close-cycle cryostat, and detected by an InGaAs detector. The probe light was obtained from a tungsten-halogen lamp analyzed with a 50 cm focal length monochromator. Further details of the sample preparation and characterization are given elsewhere [5,6,16–18,34]. 3. Results and discussion Fig. 1 shows the PR spectra of GaAsBi layers measured at 300 K. A distinct spectral feature due to GaAsBi was observed in each spectrum. The PR signal shifts to lower energies with increasing Bi content, which corresponding to the reduction of the bandgap energy. For all the layers the spin–orbit (SO) splitting is observed in PR spectra. The bandgap energies (Eg) and the optical transition between the SO splitted valence band and the conduction band (Eg + DSO) are indicated with arrows in Fig. 1. In order to determine the energies of Eg and Eg + DSO transitions a theoretical multilayer model based on the matrix method has been applied [6]. The energies of Eg and Eg + DSO transitions extracted from the fitting curves are shown in Fig. 2(a). Their evolutions decrease significantly with increasing Bi content. By subtracting the band gap energy from the SO energy, the SO splitting DSO was extracted and plotted also in Fig. 2(b). The composition dependence of the bandgap and the SO splitting of a semiconductor alloy is usually described by introducing a constant bowing parameter b. For the ternary system GaAs1xBix, the relationships are:

EGaAsBi ¼ xEGaBi þ ð1  xÞEGaAs  bg xð1  xÞ g g g

DGaAsBi SO

¼

xDGaBi SO

þ ð1 

xÞDGaAs SO

ð1aÞ

 bSO xð1  xÞ

ð1bÞ EGaBi g

where x is the bismuth content in GaAsBi alloy. ¼ 0:360 eV (Ref. [27]) and EGaAs ¼ 1:425 eV are the bandgap energies of g GaBi and GaAs, respectively. Also DGaBi ¼ 2:15 eV [3] and SO DGaAs ¼ 0:34 eV are the SO splitting energies of GaBi and GaAs, SO respectively. For the GaAsBi alloy investigated here, using a constant bowing coefficient would result in a bad fit of experimental data, especially when Bi content increases (see the dashed line in Fig. 2(b)). In order to remedy to this failure, we define a bowing parameter that decreases monotonically with increasing Bi content as follows [27]:

bg ðxÞ ¼

ag

ð2aÞ

1 þ bg x

bSO ðxÞ ¼

aSO

ð2bÞ

1 þ bSO x

By substituting Eq. (2) into Eq. (1), we get good fits as shown by solid lines in Fig. 2(a) and (b). We find ag = 6.5, bg = 35, aSO = 6 and Table 1 Growth parameters of GaAsBi alloys. The Bi content and the thickness are determined by high-resolution X-ray diffraction. Sample

GaAsBi growth temperature (°C)

GaAs buffer thickness (nm)

GaAsBi layer thickness (nm)

Bi content (%)

A B C D E F

420 420 420 420 420 420

100 80 80 80 80 80

210 160 50 125 50 50

0.2 0.7 1.3 2 3.7 4.8

Eg

Eg +Δ

300 K

SO

x=4.8

x=3.7

PR Intensity (arb.unit)

2

1.6

1.7

1.8

1.9

1.6

1.7

1.8

1.9

1.6

1.7

1.8

1.9

x=0.7

1.6

1.7

1.8

1.9

x=0.2

1.6

1.7

1.8

1.9

1.6

1.7

1.8

1.9

1.8

1.9

x=2

x=1.3

x=0 % Exp. Fit 1.0

1.2

1.6

1.4

1.7

1.6

1.8

2.0

Energy (eV) Fig. 1. Room temperature PR intensity spectra of the GaAsBi samples as a function of Bi content. The solid lines represent adjustments by a multilayer model. Arrows designate the position of Eg and Eg + DSO transitions. Parts of PR spectra from 1.6 to 1.9 eV are zoomed.

bSO = 140. This result indicates that the bowing parameter decreases with increasing Bi content. Similar results are found in GaAsN and InAsN alloys [38,39]. The composition dependence of the bowing parameter are due to the large differences between the sizes of the alloyed As and Bi atoms and between their atomic orbital energies, spatially separated and sharply localized band edge states are formed in the alloy. Our data indicate that the GaAsBi is III–V alloy exhibiting a Bi dependent bowing parameter not only for Eg, but also for DSO. Fig. 3(a) and (b) shows the temperature dependence of PL and PR spectra of GaAsBi layer with Bi = 4.8%, respectively. The measurements were performed in the temperature range of 12–300 K. At low temperatures (12–100 K), the PL spectra are dominated by only one peak located at 1.34 eV, which shows a significant reduction in the intensity as the temperature increases. As discussed in our previous work [15], this thermal quenching effect is an indicative of the presence of localized states. Such behavior is generally observed for mismatch materials such as GaAsN and GaAsBi [14,36,40]. Various procedures are required to understanding the origin of this phenomenon. The inset of Fig. 3(a) shows low temperature (12 K) PL spectra of GaAsBi sample with Bi = 4.8% measured at three incident light wavelengths of k = 514 nm, 442 nm and 325 nm. It can be observed that the peak position exhibits no change or shows small blueshift with decreasing wavelength. Depending on the wavelength, the penetration depth varies. Indeed, the penetration depth increases with increasing wavelength. However, for the lower excitation wavelength of 325 nm, PL intensity of peak located at 1.34 eV is more pronounced than the GaAs peak. On the other hand, at higher wavelength (514 nm) the PL intensity of this peak is less marked

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H. Fitouri et al. / Optical Materials xxx (2015) xxx–xxx

PR Energy (eV)

1.8

(a)

300 K

Eg

1.7

Eg+ΔSO

1.4 1.3

SO splitting (eV)

1.2 1.1 0.7

(b) Fit by substituting Eq.(2) into Eq. (1) Fit by a constant bSO = - 6 eV (Ref. 3)

0.6 0.5 0.4 0.3

0

1

2

3

4

5

Bi content (%) Fig. 2. (a) Energies of Eg and Eg + DSO transitions in GaAsBi obtained from PR spectra. (b) The SO splitting for GaAsBi extracted from the Egand Eg + DSO transitions. The dashed line is the linearly interpolated SO splitting using DGaBi ¼ 2:15 eV, and bSO ¼ 6 eV. The solid line is a fit to the experimental data SO using a Bi content dependent bowing coefficient.

than that of GaAs substrate and is strongly asymmetric and shows the coexistence of two peaks seems be related to localized and delocalized exciton recombination. By increasing incident light wavelength, the localized levels saturate, giving rise to delocalized excitons and to an increase in the full-width at half-maximum of PL peak. This is probably due to inhomogeneous broadening caused by fluctuations in the local Bi content, valence band potential, and strain distribution, and eventually band filling. This result confirms the coexistence of radiative and nonradiative centers in this alloy. Similar PL results were found in GaAsN alloys when the excitation power was increased [41]. Recently, at low temperature,

Mazzucato et al. [32] have demonstrated clear distinction between the localized and delocalized states in the spectral and temporal photoluminescence emission. Indeed, at low excitation power, the localized emission is more pronounced. However, at higher excitation power the delocalized emission become comparatively more active in the system. The PR spectral line shape does not become sharp at all in the low temperature range as reported in Fig. 3(b). An increase in PR signal with the increase in temperature is observed. It should be remarked that this variation is independent of the incident light wavelengths (not shown here). It means that this temperature-induced change in PR signal is not related to the modulation conditions, but has a direct link with the material characteristics. Fig. 4 shows the temperature dependence of transition intensity of GaAsBi alloys with Bi content above 2%. For such Bi content, a decrease in transition intensity is observed below about 100 K. However, the difference between the values of PR intensity is related to the structural quality (surface, roughness, etc.) for all samples. We have connected this behavior with PL results, which are presented in the Fig. 3(a). For the highest, 4.8% Bi, sample, an emission band associated with a recombination involving Bi-related defects is clearly visible and confirms the significant carrier localization in the layer. We can conclude that this effect has an influence on the efficiency of PR modulation. At low temperatures, where the thermal energy is small, electrons and holes induced by a pump beam can be immediately localized on some potential fluctuations. The localized carriers cannot move and they do not contribute to the changes in the band bendings and, hence, to the modulation of a built-in electric field. With an increase in temperature the thermal energy increases and the localization energy can be exceeded, what result in the possibility to move for carriers. Such behavior induces an increase in the modulation efficiency, because moving carriers allow a change in the built-in electric field. On the basis of this effect, the temperature dependence of PR transition intensity can be a good indicator of the carrier localization. The temperature dependence of the PR transition energy of the GaAs substrate and GaAsBi epilayers issued from spectra analyses

(a)

(b) 12 K 20 K 30 K 50 K

12 K 20 K

75 K

30 K

100 K

100 K 325 nm 442 nm 514 nm

1.6

T= 12 K

125 K

1.4

150 K

1.2 1.0

Delocalized states

125 K

150 K 175 K 200 K

175 K

0.8

225 K

200 K

0.6

225 K

0.4 0.2

250 K

250 K

1.1

1.2

1.3

1.4

1.5

1.0

1.1

1.2

300 K

300 K

Energy (eV)

0.9

PR Intensity (arb.unit)

75 K

PL Intensity (arb.unit)

PL Intensity (arb. unit)

50 K

1.3

Energy (eV)

1.4

1.5

1.6

1.1

1.2

1.3

1.4

1.5

1.6

1.7

Energy (eV)

Fig. 3. Temperature dependence of (a) PL spectra and (b) PR spectra of a GaAsBi with Bi = 4.8%. Inset show low temperature PL spectra of this GaAsBi layer measured at three incident light wavelengths (k = 514 nm, 442 nm and 325 nm).

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H. Fitouri et al. / Optical Materials xxx (2015) xxx–xxx

100 x = 2% x = 3.7% x = 4.8%

3.6 3.4

95 90

(meV)

3.2

2.8

300 K

2.6

12 K

3.0

85

Eg -Eg

PR transition intensity (arb.unit)

3.8

80 75

2.4 2.2

70

2.0

65

1.8 0

50

100

150

200

250

0.0

300

0.5

1.0

1.5

Temperature (K)

are plotted in Fig. 5. As can be seen from this figure, the PR transition energy shift is reduced as the Bi content increases. These spectra could be fitted by a Bose–Einstein statistical expression [42].

2 eðh=TÞ

1

þ

PR data Bose-Einstein fit

x=0.7 %

1.48 x= 1.3 %

Energy (eV)

1.40

x= 2 %

1.36 x= 3.7 %

1.32

4.0

4.5

5.0

230

ð3Þ

x= 0 %

1.44

3.5

220 210

KBT 2

where aB represents the electron–phonon interaction strength, h is the average phonon temperature, T is the temperature and KB is Boltzmann constant. The GaAsBi band gap energy measured by PR and that of GaAs were fitted by using Eq. (3). The solid curves shown in Fig. 5 are obtained from this analysis. The band gap energy shift due to temperature change can be also estimated. Fig. 6 shows the band gap energy differences between 12 and 300 K as a function of Bi content. As the Bi content increases, the band gap shift slowly decreases. Above a Bi content of 0.7%, the band gap shift energy rapidly decreases. This result indicates that the temperature dependence of the band gap energy of GaAsBi alloys decreases with increasing Bi content. However, with increasing Bi content, the band gap is less sensitive to temperature. A similar trend in the temperature dependence of the band gap was obtained in GaAsBi grown by low pressure MOVPE [43], but this conclusion is different to that found in GaAsBi grown by MBE [1] and in other dilute bismide alloys [44]. The reason for this discrepancy is not known.

1.52

3.0

240

200

αB (meV)

EðTÞ ¼ EB  aB 1 þ



2.5

Fig. 6. Band gap energy differences between 12 and 300 K as a function of Bi content.

θ (K)

Fig. 4. Temperature dependence of PR transition intensity of GaAsBi alloys with different Bi content.



2.0

Bi content (%)

55 50 45 40 35 30 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Bi content (%) Fig. 7. Electron–phonon interaction strength and average phonon energy obtained from the analysis using the Bose–Einstein statistical expression.

Fig. 7 shows the electron–phonon interaction strength and the average phonon energy obtained from the analysis using the Bose–Einstein expression. Both the electron–phonon interaction strength and the average phonon energy are found to initially decrease with introducing Bi and then increases. However, the average phonon energy obtained from the analysis is much larger than that expected from the linear interpolation between the longitudinal optical (LO) phonon energies of GaAs (293 cm1) and GaBi (215 cm1) [45,46]. The average phonon energy of GaAsBi is estimated as 140 cm1. This mode is recently observed in GaAsBi Raman studies by Steele et al. [47] and also reported by Verma et al. [45]. This suggests that the interaction between electrons localized at Bi atoms interact preferentially with the localized GaBi vibration mode. Thus, the interaction between electrons localized at Bi atoms and the GaBi localized vibration is considered to play an important role in the reduction of the temperature dependence of the band gap energy of GaAsBi alloys.

1.28 x= 4.8 %

4. Conclusion

1.24 1.20 0

50

100

150

200

250

300

Temperature (K) Fig. 5. Temperature dependence of the band gap energy for GaAsBi layers with different Bi content with fits by the Bose–Einstein (solid lines) Eq. (3).

We have studied the optical properties of GaAs1xBix grown on GaAs substrate with x up to 4.8% by PR and PL techniques. The PR modulation efficiency of GaAsBi layer decreases with decreasing temperature. This feature has been attributed to the carrier localization effect occurring in GaAsBi and has been confirmed by

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PL measurements. The temperature dependences of the band gap energy were analyzed using the Varshni expression and an expression containing the Bose–Einstein occupation factor for phonons. The temperature dependences of these band gap energies become significantly weak for GaAsBi with Bi incorporation. This suggests that the density of states around the band edge of GaAsBi is modified from that of GaAs due to the localized states possibly originated from Bi clusters. Acknowledgment The authors acknowledge financial support from DGRST. References [1] S. Francoeur, M.J. Seong, A. Mascarenhas, S. Tixier, M. Adamcyk, T. Tiedje, Appl. Phys. Lett. 82 (2003) 3874. [2] K. Oe, Jpn. J. Appl. Phys. 41 (2002) 2801. [3] B. Fluegel, S. Francoeur, A. Mascarenhas, S. Tixier, E.C. Young, T. Tiedje, Phys. Rev. Lett. 97 (2006) 067205. [4] S. Tixier, M. Adamcyk, T. Tiedje, S. Francoeur, A. Mascarenhas, P. Wei, F. Schiettekatte, Appl. Phys. Lett. 82 (2003) 2245. [5] H. Fitouri, I. Moussa, A. Rebey, A. Fouzri, B. El Jani, J. Cryst. Growth 295 (2006) 114. [6] Z. Chine, H. Fitouri, I. Zaied, A. Rebey, B. El Jani, Semicond. Sci. Technol. 25 (2010) 065009. [7] R. Kudrawiec, J. Kopaczek, P. Sitarek, J. Misiewicz, M. Henini, S.V. Novikov, J. Appl. Phys. 111 (2012) 066103. [8] K. Bertulis, A. Krotkus, G. Aleksejenko, V. Pacebutas, R. Adomavicius, G. Molis, S. Marcinkevicius, Appl. Phys. Lett. 88 (2006) 201112. [9] T. Tiedje, E.C. Young, A. Mascarenhas, Int. J. Nanotechnol. 5 (2008) 963. [10] Y. Tominaga, K. Oe, M. Yoshimoto, Appl. Phys. Express 3 (2010) 062201. [11] K. Alberi, O.D. Dubon, W. Walukiewicz, K.M. Yu, K. Bertulis, A. Krotkus, Appl. Phys. Lett. 91 (2007) 051909. [12] Z. Batool, K. Hild, T.J.C. Hosea, X. Lu, T. Tiedje, S.J. Sweeney, J. Appl. Phys. 111 (2012) 113108. [13] S. Imhof, A. Thranhardt, A. Chernikov, M. Koch, N.S. Koster, K. Kolata, S. Chatterjee, S.W. Koch, X. Lu, S.R. Johnson, D.A. Beaton, T. Tiedje, O. Rubel, Appl. Phys. Lett. 96 (2010) 131115. [14] M.K. Shakfa, D. Kalincev, X. Lu, S.R. Johnson, D.A. Beaton, T. Tiedje, A. Chernikov, S. Chatterjee, M. Koch, J. Appl. Phys. 114 (2013) 164306. [15] I. Moussa, H. Fitouri, Z. Chine, A. Rebey, B. El Jani, Semicond. Sci. Technol. 23 (2008) 125034. [16] I. Moussa, H. Fitouri, A. Rebey, B. El Jani, Thin Solid Films 516 (2008) 8372. [17] Z. Chine, H. Fitouri, I. Zaied, A. Rebey, B. El Jani, J. Cryst. Growth 330 (2011) 35. [18] H. Fitouri, I. Moussa, A. Rebey, B. El Jani, Microelectron. Eng. 88 (2011) 476. [19] R.D. Richards, F. Bastiman, C.J. Hunter, D.F. Mendes, A.R. Mohmad, J.S. Roberts, J.P.R. David, J. Cryst. Growth 390 (2014) 120. [20] K. Forghani, A. Anand, L.J. Mawst, T.F. Kuech, J. Cryst. Growth 380 (2013) 23.

5

[21] A.J. Ptak, R. France, D.A. Beaton, K. Alberi, J. Simon, A. Mascarenhas, C.S. Jiang, J. Cryst. Growth 338 (2012) 107. [22] T. Fuyuki, R. Yoshioka, K. Yoshida, M. Yoshimoto, Appl. Phys. Lett. 103 (2013) 202105. [23] X. Lu, D.A. Beaton, R.A. Lewis, T. Tiedje, M.B. Whitwick, Appl. Phys. Lett. 92 (2008) 192110. [24] V. Pacebutas, R. Butkute, B. Cechavicius, J. Kavaliauskas, A. Krotkus, Thin Solid Films 520 (2012) 6415. [25] A.R. Mohamed, F. Bastiman, J.S. Ng, S.J. Sweeney, J.P.R. David, Phys. Status Solidi C 9 (2012) 259. [26] M. Yoshimoto, S. Murata, A. Chayahara, Y. Horino, J. Saraie, K. Oe, Jpn. J. Appl. Phys. 42 (2003) L1235. [27] X. Lu, D.A. Beaton, R.B. Lewis, T. Tiedje, Y. Zhang, Appl. Phys. Lett. 95 (2009) 041903. [28] A.R.H. Carvalho, V. Orsi Gordo, H.V.A. Galeti, Y. Galvao Gobato, M.P.F. de Godoy, R. Kudrawiec, O.M. Lemine, M. Henini, J. Phys. D Appl. Phys. 47 (2014) 075103. [29] C. Gogineni, N.A. Riordan, S.R. Johnson, X. Lu, T. Tiedje, Appl. Phys. Lett. 103 (2013) 041110. [30] Y.I. Mazur, V.G. Dorogan, M. Schmidbauer, G.G. Tarasov, S.R. Johnson, X. Lu, M.E. Ware, S-Q. Yu, T. Tiedje, G.J. Salamo, J. Appl. Phys. 113 (2013) 144308. [31] G. Pettinari, A. Polimeni, M. Capizzi, J.H. Blokland, P.C.M. Christianen, J.C. Maan, E.C. Young, T. Tiedje, Appl. Phys. Lett. 92 (2008) 262105. [32] S. Mazzucato, H. Lehec, H. Carrère, H. Makhloufi, A. Arnoult, C. Fontaine, T. Amand, X. Marie, Nanoscale Res. Lett. 9 (2014) 19. [33] S. Imhof, C. Wagner, A. Thranhardt, A. Chernikov, M. Koch, N.S. Koster, S. Chatterlee, S.W. Koch, O. Rubel, X. Lu, S.R. Johnson, D.A. Beaton, T. Tiedje, Appl. Phys. Lett. 98 (2011) 161104. [34] N. Ben Sedrine, I. Moussa, H. Fitouri, A. Rebey, B. El Jani, R. Chtourou, Appl. Phys. Lett. 95 (2009) 011910. [35] R. Kudrawiec, P. Poloczek, J. Misiewicz, M. Shafi, J. Ibanez, R.H. Mari, M. Henini, M. Schmidbauer, S.V. Novikov, L. Turyanska, S.I. Molina, D.L. Sales, M.F. Chisholm, Microelectron. J. 40 (2009) 537. [36] R. Kudrawiec, G. SJk, J. Misiewicz, F. Ishikawa, A. Trampert, K.H. Ploog, Appl. Phys. Lett. 94 (2009) 011907. [37] J. Li, T.-H. Kim, K. Forghani, W. Jiao, W. Kong, K. Collar, T.F. Kuech, A.S. Brown, J. Appl. Phys. 116 (2014) 043524. [38] S.H. Wei, A. Zunger, Phys. Rev. Lett. 76 (1996) 664. [39] R. Kudrwiec, J. Misiewicz, Q. Zhuang, A.M.R. Godenir, A. Krier, Appl. Phys. Lett. 94 (2009) 151902. [40] A.R. Mohmad, F. Bastiman, C.J. Hunter, R.D. Richards, S.J. Sweeney, J.S. Ng, J.P.R. David, B.Y. Majlis, Phys. Status Solidi B 251 (2014) 1276. [41] R. Kudrwiec, G. Sk, J. Misiewicz, F. Ishikawa, A. Trampert, K.H. Ploog, Appl. Phys. Lett. 94 (2009) 011907. [42] L. Vina, S. Logothetidis, M. Cardona, Phys. Rev. B 30 (1984) 1979. [43] J. Yoshida, T. Kita, O. Wada, K. Oe, Jpn. J. Appl. Phys. 42 (2003) 371. [44] J. Kopaczek, R. Kudrawiec, W.M. Linhart, M.K. Rajpalke, K.M. Yu, T.S. Jones, M.J. Ashwin, J. Misiewicz, T.D. Veal, Appl. Phys. Lett. 103 (2013) 261907. [45] P. Verma, K. Oe, M. Yamada, H. Harima, M. Herms, G. Irmer, J. Appl. Phys. 89 (2001) 1657. [46] M.J. Seong, S. Francoeur, S. Yoon, A. Mascarenhas, S. Tixier, M. Adamcyk, T. Tiedje, Superlattices Microstruct. 37 (2005) 394. [47] J.A. Steele, R.A. Lewis, M. Henini, O.M. Lemine, A. Alkaoud, J. Appl. Phys. 114 (2013) 193516.

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