Effects of hydrogen etching on stress control in AlN interlayer inserted GaN MOVPE on Si

Abstract

Clarification and control of the hydrogen etching of GaN is essential to achieving high-quality GaN-on-Si virtual substrates and devices based on it produced by metalorganic vapor phase epitaxy. This phenomenon and its effects on GaN-on-Si stress control were studied in this work. Without deliberate protection, voids with lateral sizes on the micrometre level underneath AlN interlayers emerged in GaN. Such voids made stress balancing in GaN-on-Si systems by inserting AlN interlayers less efficient. By flowing a protective large flow rate of ammonia, voids were eliminated while GaN decomposition still happened, which led to AlGaN alloy in the interlayers. Interfaces of Ga incorporated AlN interlayers grown under large-scale varied conditions were characterised by scanning transmission electron microscopy and energy dispersive spectrometry. Higher growth temperatures caused more Ga in the interlayers and weakened their capacity to induce compressive stress in the overlying GaN.

Analysis of strain and dislocation evolution during MOCVD growth of an AlGaN/GaN power high-electron-mobility transistor structure

“…Mostly cited in the literature are two main hypotheses: gallium comes into AlN from Ga-containing deposits in the growth chamber [39][40][41] or from residual metal Ga that is caused by decomposition of the underlying GaN and remains on the surface. [42][43][44] In both cases, the effect the growth temperature is expectable and should be attributed to enhanced decomposition of GaN, either accumulated in deposits or grown prior to AlN.…”

“…Direct measurements of gallium incorporation into nominal AlN layers are available in a number of publications. [39][40][41][42][43][44] Various experimental techniques were applied either to measure the gallium content in AlN intyerlayers 41,43) or to extract the composition profiles. 39,40,42,44) These techniques include atom probe tomography, 39,40) high-resolution X-ray diffraction, 41,42) X-ray photoelectron spectroscopy, 42,43) and EDS 44) analysis.…”

“…[39][40][41][42][43][44] Various experimental techniques were applied either to measure the gallium content in AlN intyerlayers 41,43) or to extract the composition profiles. 39,40,42,44) These techniques include atom probe tomography, 39,40) high-resolution X-ray diffraction, 41,42) X-ray photoelectron spectroscopy, 42,43) and EDS 44) analysis. The main conclusions that can be drawn from these studies are: (i) unintentional gallium incorporation into Al(Ga)N spacers and interlayers occurs, and the gallium content in nominally AlN can be as high as about 50%; (ii) gallium incorporation is a strong function of the growth temperature: the higher is the temperature the more gallium incorporates into AlN; (iii) the gallium "tail" in AlN may be about or even exceed 10 nm, this length is comparable or larger than the typical thickness of AlN interlayers.…”

GaN-based power high-electron-mobility transistors on Si substrates: from materials to devices

“…(1) Theoretically, a single layer of LT-AlN of thickness 10-20 nm is sufficient to balance the thermal tensile stress of a 0.7-1 µm thick GaN-on-Si substrate, while maintaining or even improving the GaN quality [95]. To grow a thicker GaN layer without cracks on the Si substrate, an alternative technique has been developed to compensate for the tensile strain in thick GaN layers by periodically inserting LT-AlN layers [96]. Since the development of this technique, important progress has been made in terms of their thickness and crystal quality.…”

Suppressing the Initial Growth of Sidewall GaN by Modifying AlN-Coated Patterned Sapphire with KOH-Based Etchant

“…We believe this reduction is because during the growth of HTU-GaN, hydrogen was used as the carrier gas, which would etch AlN NL. 20 This etching process was a function of (1) transport of hydrogen from the main gas stream to the pattern surface, (2) surface etching reaction and (3) transfer of products back to the gas stream. Because of the pattern morphology, (1) transport of hydrogen and (3) products between the main gas stream and sidewall should be faster than between gas stream and bottom.…”