Examination of defects and the seed's critical thickness in HVPE‐GaN growth on ammonothermal GaN seed

Abstract

It is demonstrated in this paper that 1.9-mm-thick gallium nitride grown by Hydride Vapor Phase Epitaxy (HVPE) on an ammonothermally grown GaN seed can reproduce the structural, in terms of defects, properties of the seed. The etch pit density and its correlation to the threading dislocation density in the ammonothermal GaN substrate and the HVPEGaN layer is presented and analyzed. However, it has recently been observed that for HVPE-GaN thicker than 2 mm some additional defects are formed in the new grown material. Therefore, three HVPE growth runs were performed in the same experimental conditions, using three structurally identical ammonothermally grown GaN seeds of different thicknesses. The influence of the thickness of the seeds on the crystallization process and the properties of the HVPE-GaN layers is shown and discussed.

Defects in Single Crystalline Ammonothermal Gallium Nitride

“…The dislocations were determined to be of mixed type because they have a distinct appearance, a smaller etch pit than the screw dislocations, and, most importantly, pure threading edge dislocations should according to the invisibility criterion not be visible in the symmetric 0008 topograph. This result contradicts DSE experiments reporting that the pure threading edge dislocation is the dominant threading dislocation type in ammonothermal GaN . It is conceivable, that in the presence of a sufficient ambient impurity concentration, such as the abundant oxygen in the ammonothermal growth environment, the dislocation could be decorated by impurities to an extent that would lead to distortion of the symmetric (000 l ) planes and therefore to contrast in the symmetric 0008 topograph.…”

“…This result contradicts DSE experiments reporting that the pure threading edge dislocation is the dominant threading dislocation type in ammonothermal GaN. [120,121] It is conceivable, that in the presence of a sufficient ambient impurity concentration, such as the abundant oxygen in the ammonothermal growth environment, the dislocation could be decorated by impurities to an extent that would lead to distortion of the symmetric (000l) planes and therefore to contrast in the symmetric 0008 topograph. Another possibility for a threading edge dislocation with a Burgers vector of type b = 1/3<11-20> to cause contrast in a 0008 topograph is if its line direction l deviates from [0001].…”

“…The evolution of the dislocation structure is conveniently studied using crosssectional samples, but so far very few reports exist. DSE of defects in GaN grown by HVPE on ammonothermal GaN has been reported, [120] and recently the structural quality of c-plane, m-plane, and a-plane ammonothermal GaN wafers was studied by XRT using a laboratory source. [31] The evolution of the microstructure during ammonothermal growth of GaN was recently reported.…”

GaN Single Crystalline Substrates by Ammonothermal and HVPE Methods for Electronic Devices

“…The data collected for Am-GaN and HVPE-GaN grown on Am-GaN seeds show that the density of large pits (screw dislocations) varies from 10 0 to 10 1 cm −2 . In turn, the density of medium and small pits (mixed and edge dislocations) is at the level of 5 × 10 4 cm −2 [23,25]. Figure 1 allows to compare EPD on the c-plane surface of a typical Am-GaN wafer from IHPP PAS and commercially available HVPE-GaN.…”

The investigation of in situ removal of Si substrates for freestanding GaN crystals by HVPE

“…19,20 Even if the EPD of the freestanding GaN crystal obtained using in situ removal of a Si substrate fall short of EPD for homoepitaxially-grown material ($10 4 cm À2 ), its value is comparable to commercial HVPE freestanding GaN grown on Al 2 O 3 substrates (TDD < 1 Â 10 7 cm À2 ). 21 This technique will allow us to obtain freestanding GaN wafer with a large scale and low fabrication cost, thus enabling to lead to their successful commercialization. Considering the importance of the growth of freestanding GaN via in situ removal of a Si substrate, the understanding of the Si etching in HVPE should be addressed for successful implementation.…”