Heteroepitaxy of AlGaN on bulk AlN substrates for deep ultraviolet light emitting diodes

Abstract

The authors report the growth of AlGaN epilayers and deep ultraviolet (UV) light emitting diodes (LEDs) on bulk AlN substrates. Heteroepitaxial nucleation and strain relaxation are studied through controlled growth interruptions. Due to a low density of preexisting dislocations in bulk AlN, the compressive strain during AlGaN heteroepitaxy cannot be relieved effectively. The built-up of strain energy eventually induces either an elastic surface roughening or plastic deformation via generation and inclination of dislocations, depending on the stressor interlayers and growth parameters used. AlGaN LEDs on bulk AlN exhibit noticeable improvements in performance over those on sapphire, pointing to a promising substrate platform for III-nitride UV optoelectronics.

Anisotropic absorption and emission of bulk(11¯00)AlN

“…The fine structure of the free excitons related to the A transition has been reported recently. 14 In this work, a further splitting into excitons of 5 and 1 symmetries has been observed. Modeling yielded a negative spin-exchange interaction constant of j = −4 meV.…”

“…[4][5][6][7] These applications in turn triggered improvements in the growth of high-quality AlN, [8][9][10] only recently allowing us to investigate the fundamental properties of this semiconductor in unpreceded quality. For example, the full width at half maximum of donor bound-exciton recombinations in AlN could be shown to be below 500 μeV, allowing for unambiguous identification of these lines, 11,12 or the optical properties of nonpolar quantum wells in AlN barriers could be understood.…”

Development of 2" AlN Substrates Using SiC Seeds

“…The comparison of photoluminescence of the GaN layers deposited on the Al face and on the N face of the single-crystal AlN substrate showed that in the former case photoluminescence is consistent with that of the homoepitaxial Ga-face GaN while in the latter an existance of the tail localized states was found (Tamulatis et al, 2003). The studies of deep-UV emission of AlGaN quantum wells (Gaska et al, 2002) as well as AlGaN UV (Nishida et al, 2004a;Ren et al, 2007;Xi et al , 2006a) and InGaN MQW green (Cartwright et al, 2006) LEDs grown on the bulk AlN substrates and blue and UV LED on the bulk GaN substrates (Cao et al, 2004;Cao et al , 2004a;Du, Lu, Chen, Xiu, Zhang & Zheng, 2010) as well as cyan and green LEDs grown on a-plane (Detchprohm et al, 2008) and m-plane (Detchprohm et al, 2010) GaN bulk substrates prove the superiority of the native substrates, e.g., the luminescence intensity of the quantum well grown on bulk AlN was higher that that of the quantum well grown on SiC by a factor of 28, the noticeable improvement over LEDs grown on sapphire in device impedance and thermal characteristics (Ren et al , 2007a), the reduction in current-voltage differential resistance and in turn-on voltage (Paskova et al, 2010). The emission spectrum of AlGaN-based UV-LEDs on a bulk AlN substrate under the high current injection is much more stable than that of LEDs fabricated on the conventional substrate (Nishida et al, 2004a;.…”

AFM Application in III-Nitride Materials and Devices

“…17(c)) even though step flow was still maintained locally ( Fig. 17(f)) (Ren et al 2007). (b) and (e), and (e) and (f) are taken after the growth of superlattices 1, 2, and 3, respectively.…”

“…Z. Ren et al adopted a design of step-graded layers consisting of three superlattices (SLs 1, 2, and 3) with average Al compositions of 0.90, 0.73, and 0.57. Each SL was composed of ten periods of Al Ga N Å)/ Al Ga N (150 Å) (x/y=1.0/ 0.8, 0.8/ 0.65, and 0.65/ 0.50) (Ren et al, 2007). Surface morphology after the growth of SL 1 (Figs.…”