Improving microstructural quality of semipolar (112̱2) GaN on m-plane sapphire by a two-step growth process

Abstract

This letter reports a two-step growth process for improving microstructural quality of semipolar (112̱2) GaN on nitridized m-plane sapphire. The two-step growth of (112̱2) GaN, islanding growth under high pressure followed by islands coalescence under low pressure, went through a roughening-recovery process, which was found very effective in reducing the density of stacking faults and dislocations in (112̱2) GaN. The x-ray rocking curves of both on-axis and off-axis planes were narrowed down by more than 50%. The improvement of GaN quality was confirmed by a boost in blue and green optical output of semipolar (112̱2) InGaN/GaN quantum wells.

Structural anisotropy of nonpolar and semipolar InN epitaxial layers

“…19 Reports on the structural anisotropy of semipolar GaN just begun to emerge and the on-axis RC of semipolar ͑1122͒ GaN films have been recently found to also exhibit anisotropic behavior. 20 The structural anisotropy of nonpolar III-nitride films affects their optical performance and device-relevant characteristics ͑carrier mobility, degradation, etc.͒, which requires detailed study of these issues. While the structural anisotropy of nonpolar GaN films have been extensively studied 1, [14][15][16][17][21][22][23] the information on the structural characteristics of nonpolar InN is very scarce 24,25 and detailed reports exists only for films grown on GaN substrates.…”

Microstructure investigation of semi-polar (11-22) GaN overgrown on differently designed micro-rod array templates

“…Furthermore, employing shorter microrods is useful for removing additional BSFs, leading to further improvement in crystal quality. The results presented provide a very promising approach to eventually achieving (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) Semi-polar GaN, particularly in the (11-22) orientation, has emerged to be a promising candidate for fabricating both light emitting diodes (LEDs) and laser diodes (LDs) with a long wavelength beyond the blue spectral region, e.g., green and yellow, which is critical for solid state lighting, visible light communications and opto-genetics. The current status of the development of (11-22) GaN on sapphire can be referred to a topical review published very recently.…”

“…This can be achieved by carefully designing micro-rod templates. Based on transmission electron microscopy and photoluminescence measurements, it has been found that the micro-rod diameter plays a vital role in effectively reducing both the dislocation density and the basal staking fault (BSF) density of the overgrown (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN, but in different manners. The BSF density reduces monotonically with increasing the micro-rod diameter from 2 to 5 lm, and then starts to be saturated when the micro-rod diameter further increases.…”

“…The current status of the development of (11-22) GaN on sapphire can be referred to a topical review published very recently. 1 In comparison with the (0001) polar orientation, InGaN/GaN based emitters grown along the (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) direction are subjected to significantly reduced piezoelectric polarization fields, thus effectively increasing their internal quantum efficiency (IQE) by reducing the associated quantum confined stark effect (QCSE). [2][3][4] Furthermore, the (11-22) plane has been predicted to exhibit a lower indium chemical potential than either non-polar or polar surfaces, 5 making (11-22) GaN accommodate indium atoms more easily than either nonpolar or polar GaN.…”

“…Microstructure investigation of semi-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) In order to realize semi-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN based laser diodes grown on sapphire, it is necessary to further improve the crystal quality of the (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN obtained by using our overgrowth approach developed on regularly arrayed micro-rod templates [T. Wang, Semicond. Sci.…”