Growth studies of GaN and alloys on LiAlO ₂ by MOVPE

Abstract

.55. Jk, 81.15.Gh Wurtzite GaN is usually used for optoelectronic devices. Because of the growth along the polar c-axis, the strong piezoelectric and spontaneous polarizations fields result in a band bending which is responsible for the poor electron-hole overlap in quantum well structures. The growth along the m-plane direction is one possibility to deposit non-polar material and leads to efficient recombination across the entire well of the QW structure. LiAlO 2 (LAO) offers the advantage to grow GaN along the m-plane direction. This work provides the results from investigations on the deposition of GaN-based structures on LAO substrates by metal-organic chemical vapor deposition.1 Introduction There is huge interest worldwide at present in finding an alternative substrate for the GaN-based epitaxial deposition. Currently, silicon carbide (SiC) and sapphire are the most favorite wafers for the AlGaInN material system. These substrates suffer from the limitations that growth is only possible along the polar c-axis which leads to strong piezoelectric and spontaneous polarization fields. The band bending related to polarization-induced fields is responsible for the poor electron-hole overlap. To achieve highly efficient quantum well (QW) structures, growth along non-polar axes is required. The m-plane growth direction demonstrates one of the non-polar axes for the deposition of the nitrides, prevents the band bending and provides direct recombination across the whole well. LiAlO 2 (LAO) substrates, with their huge advantage of low cost and easy substrate removal, offer the possibility to grow GaN along the m-plane direction. The growth of GaN on this substrate has been investigated by several research groups [1][2][3][4][5][6][7][8][9][10][11]. This work provides the results from investigations on the deposition of GaN-based structures on LAO substrates.

Development of m-plane GaN anisotropic film properties during MOVPE growth on LiAlO2 substrates

“…In addition to that, the material is produced by the comparably cheap Czochralski pulling method. A major disadvantage of this substrate is the thermal and chemical instability which demands special care on the epitaxial process and leads to highly n-type doped films, most likely related to oxygen incorporation [4]. The growth of high-quality m-plane GaN on LiAlO 2 was already reported using various techniques as molecular beam epitaxy (MBE) [5], hydride vapour phase epitaxy (HVPE) [6] and metal organic vapour phase epitaxy (MOVPE) [7].…”

Growth and investigation of m-plane (In)GaN buffer layers on LiAlO2 substrates

“…As a starting layer, we chose Mg-doped InGaN since this material can be grown under nitrogen ambient at reasonable quality. The Mg doping serves the purpose to block oxygen from diffusing out of the substrate which will otherwise lead to a very high n-type background carrier concentration in the GaN layer [8,12]. In [4,13].…”

“…But the layers still exhibit either a low phase purity, rough surfaces or a high background carrier concentration, the latter being caused by an outdiffusion of oxygen from the substrate at elevated temperatures. As we have shown in an earlier report, the introduction of a thin layer of Mg-doped InGaN helps to effectively seal the substrate surface and to block the outdiffusion of oxygen into the layer [8]. By using this approach of growing m-plane GaN, nonpolar MQW structures with high wavelength stability could be produced [9].…”

m ‐plane GaN/InGaN/AlInN on LiAlO2 grown by MOVPE

“…Nitridation of the surface leads to the formation of a thin layer of AlN [11] while InGaN:Mg grown under N 2 ambient was found helpful to seal the surface and to enable m-plane GaN growth [3]. The layer was doped with Mg because of its oxygen blocking effects.…”