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Luminescent N-polar ( In , Ga ) N / GaN quantum wells grown by plasma-assisted molecular beam epitaxy at high temperature
| Content Provider | Semantic Scholar |
|---|---|
| Author | Chèze, Caroline Feix, Felix Lähnemann, Jonas Flissikowski, Timur Wolny, Patricia M. |
| Copyright Year | 2018 |
| Abstract | N-polar (In,Ga)N/GaN quantum wells prepared on freestanding GaN substrates by plasma-assisted molecular beam epitaxy at conventional growth temperatures of about 650 ◦C do not exhibit any detectable luminescence even at 10 K. In the present work, we investigate (In,Ga)N/GaN quantum wells grown on Gaand N-polar GaN substrates at a constant temperature of 730 ◦C. This exceptionally high temperature results in a vanishing In incorporation for the Ga-polar sample. In contrast, quantum wells with an In content of 20% and abrupt interfaces are formed on N-polar GaN. Moreover, these quantum wells exhibit a spatially homogeneous green luminescence band up to room temperature, but the intensity of this band is observed to strongly quench with temperature. Temperature-dependent photoluminescence transients show that this thermal quenching is related to a high density of nonradiative Shockley-Read-Hall centers with large capture coefficients for electrons and holes. 1 ar X iv :1 71 0. 08 35 1v 1 [ co nd -m at .m tr lsc i] 2 3 O ct 2 01 7 N-polar (i. e., [0001̄]-oriented) group-III nitride heterostructures are currently attracting interest as potential candidates for advanced electronic and optoelectronic devices. One of the unique advantages of these structures as compared to their well-established Ga-polar counterparts is the opposite direction of the polarization-induced internal electrostatic fields. Specifically, these reversed fields have the potential to improve the scalability of GaN high-frequency transistors by providing stronger electron confinement and reducing ohmic contact resistance,1 to enhance the performance of light emitting diodes by increasing the internal quantum efficiency and the carrier injection efficiency,2–5 and to increase the collection efficiency of the photocurrent in solar cells.6 Concerning light emission from N-polar (In,Ga)N/GaN quantum wells (QWs), however, a serious problem has recently been identified for samples synthesized by plasma-assisted molecular beam epitaxy (PAMBE). For homoepitaxial samples prepared on free-standing GaN substrates, no photoluminescence (PL) signal was detected even at 10 K, while the intense PL band observed for heteroepitaxial samples grown on SiC was found to originate exclusively from semipolar facets around ∨ pits induced by threading dislocations.7,8 Spatially localized emission has also been reported for samples fabricated by metal-organic chemical vapor deposition (MOCVD), in this case stemming from semipolar QWs formed around hexagonal mounds.9 Since thick (In,Ga)N layers exhibited detectable PL, Chèze et al. 7 and Fernández-Garrido et al. 8 attributed their finding to a high concentration of nonradiative point defects at the interfaces between the QWs and the barriers.7,8 The samples used for the investigations of Chèze et al. 7 and Fernández-Garrido et al. 8 were fabricated under standard conditions optimized for Ga-polar structures as also done in previous work.2,10 However, it has been established that N-polar (In,Ga)N layers can be grown at substantially higher temperatures compared to their Ga-polar counterparts.10–14 The higher thermal stability of N-polar group-III nitrides is related to their specific bonding configuration, causing surface N atoms to be more strongly bound by three back bonds to the cation layer underneath compared to the single back bond for the metalpolar case.11 Moreover, for N-polar (In,Ga)N layers grown by PAMBE, it was shown that an increase of the growth temperature from 500 to 600 ◦C enhances the PL intensity.10 In the present work, we investigate N-polar (In,Ga)N/GaN QWs synthesized at a growth temperature usually only used for bare GaN, namely, 730 ◦C.15 X-ray diffraction (XRD) profiles evidence the formation of highly uniform QWs with abrupt interfaces and an In content of 20%. The sample exhibits a PL band in the green spectral range up to room temperature. Using monochromatic catholuminescence (CL) maps, we ensure that this luminescence band originates from the N-polar QWs. Time-resolved PL measurements reveal that recombination occurs between spatially separate, individually localized elec- |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://export.arxiv.org/pdf/1710.08351 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
