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Carrier recombination under one-photon and two-photon excitation in GaN epilayers
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Micron 40 (2009) 118–121 www.elsevier.com/locate/micron
Carrier recombination under one-photon and two-photon excitation in GaN epilayers S. Miasojedovas a,*, M. Butkus a, S. Jursˇe˙nas a, B. Łucznik b, I. Grzegory b, T. Suski b b
a Institute of Material Science and Applied Research, Sauletekio 9, III building, Vilnius LT 10222, Lithuania Polish Academy of Sciences, Institute of High Pressure Physics (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland
Received 15 October 2007; received in revised form 25 January 2008; accepted 27 January 2008
Abstract Luminescence properties of 100-mm thick GaN epilayers grown by hydride vapor phase epitaxy (HVPE) over three different substrates: highpressure grown n-type bulk GaN (HP-n-GaN), high-pressure bulk GaN doped with magnesium (HP-GaN:Mg), and free-standing HVPE lifted-off from sapphire (FS-HVPE-GaN), were compared by means of one-photon and two-photon excitations. The contribution of carrier capture to nonradiative traps was estimated by the analysis of luminescence transients with carrier diffusion taken into account. The estimated values of carrier lifetime of about 3 ns and diffusion coefficient of 1 cm2/s indicate the highest quality of GaN epilayers on FS-HVPE-GaN substrates. # 2008 Elsevier Ltd. All rights reserved. Keywords: GaN; Time-resolved luminescence; Two-photon; HVPE; Diffusion
1. Introduction III-Nitride semiconductors are successfully applied for blue and UVoptoelectronic devices such as light emitting diodes and laser diodes, as well as high-voltage and high-power electronic devices (Nakamura and Fasol, 1997; Nakamura and Chichibu, 2000). Although these devices are commercially available, there are a lot of unsolved problems related to the high density of nonradiative traps in GaN epilayers. The conventional heteroepitaxial growth of GaN films results in high dislocation densities (108 to 1010 cm2) which affect both optical and electrical device properties (Morkoc¸, 2001). One of the ways to reduce threading dislocations in the film is growth of the homoepitaxial layers of large thickness by hydride vapor phase epitaxy (HVPE) (Frayssinet et al., 2002). In recent decade, significant progress has been achieved in growth of GaN layers, which has an impact on dominating luminescence decay processes (Morkoc¸, 2001). For the surface excited (one-photon, 1-P) high quality GaN layers, due to efficient diffusion created carriers rapidly escape from the
* Corresponding author at: Institute of Material Science and Applied Research, Sauletekio ave. 9, III building 705, Vilnius 10222, Lithuania. Tel.: +370 5 2366028. E-mail address: [email protected] (S. Miasojedovas). 0968-4328/$ – see front matter # 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.micron.2008.01.011
excited region, thus luminescence lifetime cannot be treated as materials quality factor anymore. Recently, we proposed application of two-photon (2-P) excitation conditions for luminescence characterization of high quality GaN (Jursˇe˙nas et al., 2006). In this article we present a study of dense electron hole plasma (EHP) recombination in HVPE grown GaN epilayers over three different substrates for 1-P surface and 2-P bulk-like excitations. 2. Materials and methods Three samples used in the present studies were prepared by HVPE method. A standard horizontal home-made quartz reactor was employed here. Approximately 100-mm thick GaN epilayers were grown over three different substrates: highpressure grown n-type bulk GaN (HP-n-GaN), high-pressure bulk GaN doped with magnesium (HP-GaN:Mg), and freestanding HVPE lifted-off from sapphire (FS-HVPE-GaN). Samples are characterized by dislocation density of the order of 105 to 106 cm2, 104 to 105 cm2, and approximately 107 cm2, respectively, revealed by defect selective etching (etch pit density) method. The samples were excited by the fourth and the second harmonic (photon energy 4.66 eV and 2.33 eV, respectively) of the actively passively mode-locked YAG:Nd3+ laser (pulse duration 25 ps, repetition rate 10 Hz). The size of the excitation
S. Miasojedovas et al. / Micron 40 (2009) 118–121
spot was approximately 1 mm. Photoluminescence was collected in back-scattering geometry and dispersed by a 0.4-m grating monochromator. A toluene optical Kerr shutter was used for temporal resolution (25 ps) of luminescence. The experiments were carried out at room temperature. 3. Discussion Fig. 1(a) displays time-integrated luminescence spectra of FS-HVPE-GaN for 1-P excitation for various excitation energy densities. For 1-P excitation the thickness of the excited region is small with the characteristic depth (Levinshtein et al., 2001) 4 a1 cm at hnP = 4.66 eV and the created carrier exc ¼ 0:15 10 density is of the order of 1019 cm2 for the excitation energy density IP of 1 mJ/cm2. For 1-P excitation (Fig. 1a) the emission spectra contain one broad luminescence band which is dominating in a wide range of excitation energy densities and peaked close to the bandgap energy of GaN (3.4 eV). The observed luminescence is typical of radiative recombination of dense electron–hole plasma (Jursˇe˙nas et al., 2001, 2005; Binet et al., 1999). This is proved by a quadratic dependence of the spectrally integrated emission intensity on excitation density, I LU / IP2 , which transforms to a linear dependence, ILU / IP for higher excitation densities (IP > 2 mJ/cm2) (not shown). Such dynamics is typical for a highly photoexcited semiconductor when bimolecular band-to-band recombination (ILU / n2) is the dominating mechanism of the emission at high excitation density. The thickness of the excited region is significantly higher for 2-P excitation (more than 103 times as compared to the case of 1-P excitation) and also characteristic depth depends on the excitation intensity (Pacˇebutas et al., 2001). For the highest 2-P excitation energy density the nonequilibrium carrier density reaches values as high as 1018 cm2. The emission spectra of FS-HVPE-GaN for 2-P high excitation (Fig. 1b) contain the
119
same luminescence band of the EHP, which is redshifted due to reabsorbtion (the band originates at about 3.3 eV). At applied high 2-P excitation conditions bimolecular band-to-band recombination dominates in the emission of the GaN epilayer. While in whole carrier recombination process, which accounts both for radiative and nonradiative processes, dominate linear nonradiative recombination. This is supported by the evident I LU / IP4 dependence of the emission band at 3.3 eV (Jursˇe˙nas et al., 2006). The domination of the linear recombination process in the entire range of the excitation densities for 2-P bulk-like excitation can accounted for lower plasma density, that is created for 2-P excitation. The transients of luminescence can reveal important information on materials quality since they reflect the dominating carrier recombination process. The luminescence transients of highly photoexcited GaN can be understood in the frames of a two-dimensional spatial-temporal model of photoexcited carrier recombination and diffusion (Jursˇe˙nas et al., 2006). The luminescence signal is integrated within the thickness of the epilayer by taking into account the possible processes of reabsorbance (with characteristic depth a1 LU ¼ 2:5 104 cm at the emission photon energy 3.4 eV Levinshtein et al., 2001). The temporal and in-depth spatial distribution of the plasma density was calculated by solving a twodimensional differential equation (Jursˇe˙nas et al., 2006). Fig. 2 shows luminescence transients obtained for 1P (a) and 2P excitation. The most striking result is shortening of the luminescence decay time for 1-P surface excitation. We attribute this fast initial decay to the impact of carrier diffusion in high quality GaN (Levinshtein et al., 2001). Since diffusion processes can be neglected for 2-P bulk-like excitation, the luminescence transients recorded for three GaN HVPE-grown epilayers deposited on various GaN substrates, directly indicate on carrier lifetime (Malinauskas et al., 2006a). The lines in Fig. 2(b) show the results of the fit for the
Fig. 1. Time-integrated luminescence spectra of HVPE GaN grown over free-standing HVPE lifted-off from sapphire substrate obtained at various excitation energy densities (a) for one-photon excitation; (b) for two-photon excitation.
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Fig. 2. Luminescence transients of HVPE GaN layers grown on different substrates (a) measured with one-photon excitation and registered at 3.4 eV; (b) measured with two-photon excitation and registered at 3.3 eV. Lines are result of fitting.
luminescence transients with the variation of a single parameter, namely carrier capture time: t = 3000 ps (for GaN layer deposited on HP-GaN:Mg), t = 3300 ps (for GaN layer deposited on FS-HVPE-GaN), and t = 1250 ps (for GaN layer deposited on HP-n-GaN). It should be noted that due to different defect structure the observed carrier lifetime slightly varies at different places of the sample surface and here we present the highest observed values. By taking into account the results obtained for 2-P excitation, one can extract the carrier diffusion values from 1-P surface excitation measurements (Fig. 2a) (Jursˇe˙nas et al., 2006). The HVPE layer grown on FS-HVPE-GaN substrate exhibits the largest D = 1.2 cm2/s (Fig. 2a, triangles); HVPE layer grown over unintentionally doped HP-n-GaN substrate shows significantly faster luminescence decay with a smaller value tLU = 600 ps and thus the lowest value of diffusion coefficient D = 0.8 cm2/s (Fig. 2a, squares); while the HVPE layer deposited over HP-GaN:Mg substrate shows an intermediate value of D = 1 cm2/s (Fig. 2a, circles). The value of D 1 cm2/s is typical for high-quality GaN (Malinauskas et al., 2006b). For these calculations br = 2 1011 cm3/s (Hangleiter et al., 1996) were employed. 4. Conclusions A study of dense EHP recombination in a HVPE grown GaN epilayers was performed under high-excitation conditions for 1-P surface and 2-P bulk-like excitations. The domination of radiative band-to-band recombination in the emission of high quality GaN was proved by a square- and quaternary-law dependence of the luminescence intensity on excitation energy density for 1-P and 2-P excitation, respectively. The luminescence decay transients obtained for 1-P and 2-P excitations were shown to be in a good agreement with a two-dimensional spatial-temporal model of photoexcited carrier recombination and diffusion under condition of saturated deep traps. The 2-P excitation regime was shown to be useful for estimation of the intrinsic carrier capture time t,
while the complementary experiment performed for 1-P surface excitation allowed for the estimation of the value of the bipolar in-depth diffusion coefficient. The highest value of carrier capture time t = 3300 ps and coefficient of bipolar diffusion D = 1.2 cm2/s. Similar behavior showed epilayer grown on high-pressure GaN doped by Mg substrate. While the sample grown on n-type high-pressure GaN showed significantly lower value of luminescence lifetime and diffusion coefficient. This shortening of luminescence lifetime we attribute not only to high density of threading dislocations but also for point defects. Acknowledgements The research at Vilnius University was partially supported by the Lithuanian State Science and Education Foundation and European Commission supported SELITEC center Contract No. G5MA-CT-2002-04047. The work at UNIPRESS/Warsaw was partially supported by the European Commission project ‘‘GaNano’’ STREP No. 505541-1. References Binet, F., Duboz, J.Y., Off, J., Scholz, F., 1999. High-excitation photoluminescence in GaN: hot-carrier effects and the Mott transition. Phys. Rev. B 60, 4715–4722. Frayssinet, E., Beaumont, B., Faurie, J.P., Gibart, P., Makkai, Z., Pe´cz, B., Lefebvre, P., Valvin, P., 2002. Micro epitaxial lateral overgrowth of GaN/ sapphire by metal organic vapour phase epitaxy. MRS Internet J. Nitride Semicond. Res. 7, 8. Hangleiter, A., Im, J.S., Forner, T., Ha¨rle, V., Scholz, F., 1996. Near-bandgap photoluminescence decay time in GaN epitaxial layers grown on sapphire. Mater. Res. Soc. Symp. Proc. 395, 559–563. Jursˇe˙nas, S., Kurilcˇik, G., Kurilcˇik, N., Zˇukauskas, A., Prystawko, P., Leszczynski, M., Suski, T., Perlin, P., Grzegory, I., Porowski, S., 2001. Decay of stimulated and spontaneous emission in highly excited homoepitaxial GaN. App. Phys. Lett. 78, 3776–3778. Jursˇe˙nas, S., Miasojedovas, S., Zˇukauskas, A., 2005. Rate of radiative and nonradiative recombination in bulk GaN grown by various techniques. J. Cryst. Growth 281, 161–167. Jursˇe˙nas, S., Miasojedovas, S., Zˇukauskas, A., Lucznik, B., Grzegory, I., Suski, T., 2006. Carrier recombination and diffusion in GaN revealed by transient
S. Miasojedovas et al. / Micron 40 (2009) 118–121 luminescence under one-photon and two-photon excitation. App. Phys. Lett. 89, 172119. Levinshtein, M.E., Rumyantsev, S.L., Shur, M.S., 2001. Properties of Advanced Semiconductor Materials GaN, AlN, InN, BN, SiC, SiGe. Wiley, New York. Malinauskas, T., Jarasˇiu¯nas, K., Miasojedovas, S., Jursˇe˙nas, S., Beaumont, B., Gibart, P., 2006a. Optical monitoring of nonequilibrium carrier lifetime in freestanding GaN by time-resolved four-wave mixing and photoluminescence techniques. App. Phys. Lett. 88, 202109–202112. Malinauskas, T., Jarasˇiu¯nas, K., Aleksieju¯nas, R., Gogova, D., Monemar, B., Beumont, B., Gibart, P., 2006b. Contribution of dislocations to carrier
121
recombination and transport in highly excited ELO and HVPE GaN layers. Phys. Status Solidi B 243, 1426. Morkoc¸, H., 2001. Comprehensive characterization of hydride VPE grown GaN layers and templates. Mater. Sci. Eng. R33, 135–207. Nakamura, S., Chichibu, S.F., 2000. Introduction to Nitride Semiconductor Blue Lasers and Light Emitting Diodes. Taylor & Francis, London. Nakamura, S., Fasol, G., 1997. The Blue Laser Diode: GaN Based Light Emitters and Lasers. Springer, Berlin. Pacˇebutas, V., Stalnionis, A., Krotkus, A., Suski, T., Perlin, P., Leszczynski, M., 2001. Picosecond Z-scan measurements on bulk GaN crystals. App. Phys. Lett. 78, 4118.
Micron 40 (2009) 118–121 www.elsevier.com/locate/micron
Carrier recombination under one-photon and two-photon excitation in GaN epilayers S. Miasojedovas a,*, M. Butkus a, S. Jursˇe˙nas a, B. Łucznik b, I. Grzegory b, T. Suski b b
a Institute of Material Science and Applied Research, Sauletekio 9, III building, Vilnius LT 10222, Lithuania Polish Academy of Sciences, Institute of High Pressure Physics (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland
Received 15 October 2007; received in revised form 25 January 2008; accepted 27 January 2008
Abstract Luminescence properties of 100-mm thick GaN epilayers grown by hydride vapor phase epitaxy (HVPE) over three different substrates: highpressure grown n-type bulk GaN (HP-n-GaN), high-pressure bulk GaN doped with magnesium (HP-GaN:Mg), and free-standing HVPE lifted-off from sapphire (FS-HVPE-GaN), were compared by means of one-photon and two-photon excitations. The contribution of carrier capture to nonradiative traps was estimated by the analysis of luminescence transients with carrier diffusion taken into account. The estimated values of carrier lifetime of about 3 ns and diffusion coefficient of 1 cm2/s indicate the highest quality of GaN epilayers on FS-HVPE-GaN substrates. # 2008 Elsevier Ltd. All rights reserved. Keywords: GaN; Time-resolved luminescence; Two-photon; HVPE; Diffusion
1. Introduction III-Nitride semiconductors are successfully applied for blue and UVoptoelectronic devices such as light emitting diodes and laser diodes, as well as high-voltage and high-power electronic devices (Nakamura and Fasol, 1997; Nakamura and Chichibu, 2000). Although these devices are commercially available, there are a lot of unsolved problems related to the high density of nonradiative traps in GaN epilayers. The conventional heteroepitaxial growth of GaN films results in high dislocation densities (108 to 1010 cm2) which affect both optical and electrical device properties (Morkoc¸, 2001). One of the ways to reduce threading dislocations in the film is growth of the homoepitaxial layers of large thickness by hydride vapor phase epitaxy (HVPE) (Frayssinet et al., 2002). In recent decade, significant progress has been achieved in growth of GaN layers, which has an impact on dominating luminescence decay processes (Morkoc¸, 2001). For the surface excited (one-photon, 1-P) high quality GaN layers, due to efficient diffusion created carriers rapidly escape from the
* Corresponding author at: Institute of Material Science and Applied Research, Sauletekio ave. 9, III building 705, Vilnius 10222, Lithuania. Tel.: +370 5 2366028. E-mail address: [email protected] (S. Miasojedovas). 0968-4328/$ – see front matter # 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.micron.2008.01.011
excited region, thus luminescence lifetime cannot be treated as materials quality factor anymore. Recently, we proposed application of two-photon (2-P) excitation conditions for luminescence characterization of high quality GaN (Jursˇe˙nas et al., 2006). In this article we present a study of dense electron hole plasma (EHP) recombination in HVPE grown GaN epilayers over three different substrates for 1-P surface and 2-P bulk-like excitations. 2. Materials and methods Three samples used in the present studies were prepared by HVPE method. A standard horizontal home-made quartz reactor was employed here. Approximately 100-mm thick GaN epilayers were grown over three different substrates: highpressure grown n-type bulk GaN (HP-n-GaN), high-pressure bulk GaN doped with magnesium (HP-GaN:Mg), and freestanding HVPE lifted-off from sapphire (FS-HVPE-GaN). Samples are characterized by dislocation density of the order of 105 to 106 cm2, 104 to 105 cm2, and approximately 107 cm2, respectively, revealed by defect selective etching (etch pit density) method. The samples were excited by the fourth and the second harmonic (photon energy 4.66 eV and 2.33 eV, respectively) of the actively passively mode-locked YAG:Nd3+ laser (pulse duration 25 ps, repetition rate 10 Hz). The size of the excitation
S. Miasojedovas et al. / Micron 40 (2009) 118–121
spot was approximately 1 mm. Photoluminescence was collected in back-scattering geometry and dispersed by a 0.4-m grating monochromator. A toluene optical Kerr shutter was used for temporal resolution (25 ps) of luminescence. The experiments were carried out at room temperature. 3. Discussion Fig. 1(a) displays time-integrated luminescence spectra of FS-HVPE-GaN for 1-P excitation for various excitation energy densities. For 1-P excitation the thickness of the excited region is small with the characteristic depth (Levinshtein et al., 2001) 4 a1 cm at hnP = 4.66 eV and the created carrier exc ¼ 0:15 10 density is of the order of 1019 cm2 for the excitation energy density IP of 1 mJ/cm2. For 1-P excitation (Fig. 1a) the emission spectra contain one broad luminescence band which is dominating in a wide range of excitation energy densities and peaked close to the bandgap energy of GaN (3.4 eV). The observed luminescence is typical of radiative recombination of dense electron–hole plasma (Jursˇe˙nas et al., 2001, 2005; Binet et al., 1999). This is proved by a quadratic dependence of the spectrally integrated emission intensity on excitation density, I LU / IP2 , which transforms to a linear dependence, ILU / IP for higher excitation densities (IP > 2 mJ/cm2) (not shown). Such dynamics is typical for a highly photoexcited semiconductor when bimolecular band-to-band recombination (ILU / n2) is the dominating mechanism of the emission at high excitation density. The thickness of the excited region is significantly higher for 2-P excitation (more than 103 times as compared to the case of 1-P excitation) and also characteristic depth depends on the excitation intensity (Pacˇebutas et al., 2001). For the highest 2-P excitation energy density the nonequilibrium carrier density reaches values as high as 1018 cm2. The emission spectra of FS-HVPE-GaN for 2-P high excitation (Fig. 1b) contain the
119
same luminescence band of the EHP, which is redshifted due to reabsorbtion (the band originates at about 3.3 eV). At applied high 2-P excitation conditions bimolecular band-to-band recombination dominates in the emission of the GaN epilayer. While in whole carrier recombination process, which accounts both for radiative and nonradiative processes, dominate linear nonradiative recombination. This is supported by the evident I LU / IP4 dependence of the emission band at 3.3 eV (Jursˇe˙nas et al., 2006). The domination of the linear recombination process in the entire range of the excitation densities for 2-P bulk-like excitation can accounted for lower plasma density, that is created for 2-P excitation. The transients of luminescence can reveal important information on materials quality since they reflect the dominating carrier recombination process. The luminescence transients of highly photoexcited GaN can be understood in the frames of a two-dimensional spatial-temporal model of photoexcited carrier recombination and diffusion (Jursˇe˙nas et al., 2006). The luminescence signal is integrated within the thickness of the epilayer by taking into account the possible processes of reabsorbance (with characteristic depth a1 LU ¼ 2:5 104 cm at the emission photon energy 3.4 eV Levinshtein et al., 2001). The temporal and in-depth spatial distribution of the plasma density was calculated by solving a twodimensional differential equation (Jursˇe˙nas et al., 2006). Fig. 2 shows luminescence transients obtained for 1P (a) and 2P excitation. The most striking result is shortening of the luminescence decay time for 1-P surface excitation. We attribute this fast initial decay to the impact of carrier diffusion in high quality GaN (Levinshtein et al., 2001). Since diffusion processes can be neglected for 2-P bulk-like excitation, the luminescence transients recorded for three GaN HVPE-grown epilayers deposited on various GaN substrates, directly indicate on carrier lifetime (Malinauskas et al., 2006a). The lines in Fig. 2(b) show the results of the fit for the
Fig. 1. Time-integrated luminescence spectra of HVPE GaN grown over free-standing HVPE lifted-off from sapphire substrate obtained at various excitation energy densities (a) for one-photon excitation; (b) for two-photon excitation.
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Fig. 2. Luminescence transients of HVPE GaN layers grown on different substrates (a) measured with one-photon excitation and registered at 3.4 eV; (b) measured with two-photon excitation and registered at 3.3 eV. Lines are result of fitting.
luminescence transients with the variation of a single parameter, namely carrier capture time: t = 3000 ps (for GaN layer deposited on HP-GaN:Mg), t = 3300 ps (for GaN layer deposited on FS-HVPE-GaN), and t = 1250 ps (for GaN layer deposited on HP-n-GaN). It should be noted that due to different defect structure the observed carrier lifetime slightly varies at different places of the sample surface and here we present the highest observed values. By taking into account the results obtained for 2-P excitation, one can extract the carrier diffusion values from 1-P surface excitation measurements (Fig. 2a) (Jursˇe˙nas et al., 2006). The HVPE layer grown on FS-HVPE-GaN substrate exhibits the largest D = 1.2 cm2/s (Fig. 2a, triangles); HVPE layer grown over unintentionally doped HP-n-GaN substrate shows significantly faster luminescence decay with a smaller value tLU = 600 ps and thus the lowest value of diffusion coefficient D = 0.8 cm2/s (Fig. 2a, squares); while the HVPE layer deposited over HP-GaN:Mg substrate shows an intermediate value of D = 1 cm2/s (Fig. 2a, circles). The value of D 1 cm2/s is typical for high-quality GaN (Malinauskas et al., 2006b). For these calculations br = 2 1011 cm3/s (Hangleiter et al., 1996) were employed. 4. Conclusions A study of dense EHP recombination in a HVPE grown GaN epilayers was performed under high-excitation conditions for 1-P surface and 2-P bulk-like excitations. The domination of radiative band-to-band recombination in the emission of high quality GaN was proved by a square- and quaternary-law dependence of the luminescence intensity on excitation energy density for 1-P and 2-P excitation, respectively. The luminescence decay transients obtained for 1-P and 2-P excitations were shown to be in a good agreement with a two-dimensional spatial-temporal model of photoexcited carrier recombination and diffusion under condition of saturated deep traps. The 2-P excitation regime was shown to be useful for estimation of the intrinsic carrier capture time t,
while the complementary experiment performed for 1-P surface excitation allowed for the estimation of the value of the bipolar in-depth diffusion coefficient. The highest value of carrier capture time t = 3300 ps and coefficient of bipolar diffusion D = 1.2 cm2/s. Similar behavior showed epilayer grown on high-pressure GaN doped by Mg substrate. While the sample grown on n-type high-pressure GaN showed significantly lower value of luminescence lifetime and diffusion coefficient. This shortening of luminescence lifetime we attribute not only to high density of threading dislocations but also for point defects. Acknowledgements The research at Vilnius University was partially supported by the Lithuanian State Science and Education Foundation and European Commission supported SELITEC center Contract No. G5MA-CT-2002-04047. The work at UNIPRESS/Warsaw was partially supported by the European Commission project ‘‘GaNano’’ STREP No. 505541-1. References Binet, F., Duboz, J.Y., Off, J., Scholz, F., 1999. High-excitation photoluminescence in GaN: hot-carrier effects and the Mott transition. Phys. Rev. B 60, 4715–4722. Frayssinet, E., Beaumont, B., Faurie, J.P., Gibart, P., Makkai, Z., Pe´cz, B., Lefebvre, P., Valvin, P., 2002. Micro epitaxial lateral overgrowth of GaN/ sapphire by metal organic vapour phase epitaxy. MRS Internet J. Nitride Semicond. Res. 7, 8. Hangleiter, A., Im, J.S., Forner, T., Ha¨rle, V., Scholz, F., 1996. Near-bandgap photoluminescence decay time in GaN epitaxial layers grown on sapphire. Mater. Res. Soc. Symp. Proc. 395, 559–563. Jursˇe˙nas, S., Kurilcˇik, G., Kurilcˇik, N., Zˇukauskas, A., Prystawko, P., Leszczynski, M., Suski, T., Perlin, P., Grzegory, I., Porowski, S., 2001. Decay of stimulated and spontaneous emission in highly excited homoepitaxial GaN. App. Phys. Lett. 78, 3776–3778. Jursˇe˙nas, S., Miasojedovas, S., Zˇukauskas, A., 2005. Rate of radiative and nonradiative recombination in bulk GaN grown by various techniques. J. Cryst. Growth 281, 161–167. Jursˇe˙nas, S., Miasojedovas, S., Zˇukauskas, A., Lucznik, B., Grzegory, I., Suski, T., 2006. Carrier recombination and diffusion in GaN revealed by transient
S. Miasojedovas et al. / Micron 40 (2009) 118–121 luminescence under one-photon and two-photon excitation. App. Phys. Lett. 89, 172119. Levinshtein, M.E., Rumyantsev, S.L., Shur, M.S., 2001. Properties of Advanced Semiconductor Materials GaN, AlN, InN, BN, SiC, SiGe. Wiley, New York. Malinauskas, T., Jarasˇiu¯nas, K., Miasojedovas, S., Jursˇe˙nas, S., Beaumont, B., Gibart, P., 2006a. Optical monitoring of nonequilibrium carrier lifetime in freestanding GaN by time-resolved four-wave mixing and photoluminescence techniques. App. Phys. Lett. 88, 202109–202112. Malinauskas, T., Jarasˇiu¯nas, K., Aleksieju¯nas, R., Gogova, D., Monemar, B., Beumont, B., Gibart, P., 2006b. Contribution of dislocations to carrier
121
recombination and transport in highly excited ELO and HVPE GaN layers. Phys. Status Solidi B 243, 1426. Morkoc¸, H., 2001. Comprehensive characterization of hydride VPE grown GaN layers and templates. Mater. Sci. Eng. R33, 135–207. Nakamura, S., Chichibu, S.F., 2000. Introduction to Nitride Semiconductor Blue Lasers and Light Emitting Diodes. Taylor & Francis, London. Nakamura, S., Fasol, G., 1997. The Blue Laser Diode: GaN Based Light Emitters and Lasers. Springer, Berlin. Pacˇebutas, V., Stalnionis, A., Krotkus, A., Suski, T., Perlin, P., Leszczynski, M., 2001. Picosecond Z-scan measurements on bulk GaN crystals. App. Phys. Lett. 78, 4118.