Defect reduction in overgrown semi-polar (11-22) GaN on a regularly arrayed micro-rod array template

Abstract

We demonstrate a great improvement in the crystal quality of our semi-polar (11-22) GaN overgrown on regularly arrayed micro-rod templates fabricated using a combination of industry-matched photolithography and dry-etching techniques. As a result of our micro-rod configuration specially designed, an intrinsic issue on the anisotropic growth rate which is a great challenge in conventional overgrowth technique for semi-polar GaN has been resolved. Transmission electron microscopy measurements show a different mechanism of defect reduction from conventional overgrowth techniques and also demonstrate major advantages of our approach. The dislocations existing in the GaN micro-rods are effectively blocked by both a SiO2 mask on the top of each GaN micro-rod and lateral growth along the c-direction, where the growth rate along the c-direction is faster than that along any other direction. Basal stacking faults (BSFs) are also effectively impeded, leading to a distribution of BSF-free regions periodically spaced by BSF regions along the [-1-123] direction, in which high and low BSF density areas further show a periodic distribution along the [1-100] direction. Furthermore, a defect reduction model is proposed for further improvement in the crystalline quality of overgrown (11-22) GaN on sapphire.

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.…”

“…6 These extended defects are expected to affect the optical performance of semi-polar GaN based devices. In order to address these material challenges, our group has developed a cost-effective approach of overgrowth on regularly arrayed micro-rod templates and thus has achieved semi-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)) GaN on sapphire with significantly improved crystal quality. Based on such overgrown semi-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)) GaN, we have demonstrated highperformance semi-polar InGaN LEDs with an emission wavelength of up to the amber spectral region.…”

“…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.…”