Z. R. Zytkiewicz

Laterally overgrown structures as substrates for lattice mismatched epitaxy

This article provides a general review of the epitaxial lateral overgrowth (ELO) technology and of application of ELO layers as substrates with adjustable value of lattice constant. In particular, the issues of ELO growth mechanism, substrate defect filtration during ELO procedure and strain in ELO layers will be addressed. Recent literature data on MOVPE ELO growth of GaN on sapphire and our results on lateral overgrowth of GaAs on GaAs and Si substrates by LPE are used as examples. Finally, other lateral overgrowth techniques (growth of lattice mismatched bridge layers and pendeo-epitaxy) will be presented and compared with the conventional ELO technique.

Influence of substrate nitridation temperature on epitaxial alignment of GaN nanowires to Si(111) substrate

An arrangement of self-assembled GaN nanowires (NWs) grown by plasma-assisted molecular beam epitaxy on a Si(111) substrate is studied as a function of the temperature at which the substrate is nitridized before GaN growth. We show that the NWs grow with the c-axis perpendicular to the substrate surface independently of nitridation temperature with only a slight improvement in tilt coherency for high nitridation temperatures. A much larger influence of the substrate nitridation process on the in-plane arrangement of NWs is found. For high (850 °C) and medium (450 °C) nitridation temperatures angular twist distributions are relatively narrow and NWs are epitaxially aligned to the substrate in the same way as commonly observed in GaN on Si(111) planar layers with an AlN buffer. However, if the substrate is nitridized at low temperature (~150 °C) the epitaxial relationship with the substrate is lost and an almost random in-plane orientation of GaN NWs is observed. These results are correlated with a microstructure of silicon nitride film created on the substrate as the result of the nitridation procedure.

Epitaxial Lateral Overgrowth of GaAs: Principle and Growth Mechanism

The results on growth mechanism of GaAs layers by epitaxial lateral overgrowth (ELO) technique from the liquid phase are reviewed. In particular, effects of melt supersaturation, seed orientation, density of surface steps and growth temperature on properties of ELO layers are discussed. It is shown that the results obtained are not a specific attribute of LPE ELO growth of GaAs layers on GaAs substrates but represent a more general phenomena encountered during the ELO growth of other epitaxial systems.

STRAIN IN GAAS LAYERS GROWN BY LIQUID PHASE EPITAXIAL LATERAL OVERGROWTH

High resolution x-ray diffraction has been used to study strain in GaAs layers grown on GaAs substrates by the liquid phase epitaxial lateral overgrowth (ELO) technique. We show that the lattice and thermal expansion coefficient mismatch between the subsequent layers and the substrate, as well as the built-in strain in the SiO2 masking film, lead to long-range deformations (macroscopic bending) extending over the whole area of the sample. Moreover, we show evidences that microscopic bending of individual ELO stripes takes place due to adhesion of their laterally overgrown parts to the masking film.

Thermal strain in GaAs layers grown by epitaxial lateral overgrowth on Si substrates

X-ray diffraction was used to study deformation of GaAs layers grown on Si substrates by liquid phase epitaxial lateral overgrowth (ELO). We show that, in the direction perpendicular to seeding lines, the GaAs ELO stripes bend outwards from the mask due to the tensile strain in the GaAs buffer layer. As narrow as 94 arcsec (004) rocking curves have been measured for the laterally grown parts of ELO stripes what indicates the high quality of ELO GaAs layers grown on GaAs-coated Si substrates. We use our model of strain relaxation via bending of laterally grown parts of ELO layers to explain some recently published results on bending of ELO GaN layers on SiC and sapphire substrates.

Influence of convection on the composition profiles of thick GaAlAs layers grown by liquid phase electroepitaxy

Abstract Liquid phase electroepitaxy (LPEE) — the method of current controlled layer growth from a solution at constant temperature — was used to grow thick GaAlAs layers on GaAs substrates. We have shown that in the presence of convection in the solution, compositionally uniform layers can be grown despite compositional nonuniformity of the source material used. Layers grown in the absence of convection had an Al content which increased with thickness. This reflects the composition profile of the source material prepared by the cooling down of the system.

Microscopic bending of GaAs layers grown by epitaxial lateral overgrowth

X-ray diffraction has been used to study the influence of the mask material on properties of GaAs layers grown by the liquid phase epitaxial lateral overgrowth (ELO) on (100) GaAs substrates. We show that ELO stripes bend towards the SiO2 mask in the direction perpendicular to seeding lines in a similar way to that as studied recently by x-ray topography for Si lamellae [H. Raidt, R. Kohler, F. Banhart, B. Jenichen, A. Gutjahr, M. Konuma, I. Silier, and E. Bauser, J. Appl. Phys. 80, 4101 (1996)]. The bending disappears when the mask is removed by selective etching. This microscopic bending is reduced by nearly 2 orders of magnitude when graphite instead of SiO2 is used to mask the substrate.

Structure of the DX state formed by donors in (Al,Ga)As and Ga(As,P)

High‐resolution Laplace‐transform deep level transient spectroscopy has been used to study the influence of the defect local environment on electron emission from the DX centers related to group‐IV (silicon) donors in AlxGa1−xAs (0.20<x<0.76) and δ‐doped GaAs and group‐VI (tellurium) donor elements in AlxGa1−xAs (0.25<x<0.73) and GaAs0.35P0.65. The experimental evidence that substitutional–interstitial atom motion is responsible for DX behavior and for the associated metastability effects is presented. The atom which is subjected to this transition is for DX(Si) silicon itself, as in the spectra only one group of peaks in AlxGa1−xAs is observed, while for DX(Te) it can be either gallium or aluminum, producing two groups of peaks in AlxGa1−x As and three or four broad emission bands in GaAs0.35P0.65. The present results rule out a possibility that the DX‐type defect states are formed by a donor atom in a stable substitutional position with a small lattice relaxation or with a fully symmetric large lattice ...

Control of adhesion to the mask of epitaxial laterally overgrown GaAs layers

Strain commonly observed in layers grown by epitaxial lateral overgrowth (ELO) and arising from interaction of the layers with the mask underneath is studied. We show that GaAs ELO layers grown by liquid-phase epitaxy on SiO2-coated GaAs substrates are strain free if the laterally overgrown parts (“wings”) of the layers hang over and have no direct contact with the mask. In other cases, tilting of the wings can be efficiently tailored by controlling the ratio of vertical to lateral growth rates at the beginning of ELO growth. In particular, this has been achieved by growing GaAs ELO layers on SiO2-coated GaAs substrates with increasing density of dislocations. Then, the ratio of vertical to lateral growth rates at the beginning of the growth is increased which in turn leads to reduction of the adhesion-induced bending of the ELO wings, as we observe by high-resolution x-ray diffraction. In the limiting case of heavily dislocated substrates, namely, on GaAs-coated Si, the vertical growth of GaAs ELO is so ...

Compositional control of thick Ga1 - xAl ϰ As layers (x≤0.72) grown by liquid phase electroepitaxy

Abstract The results of electroepitaxial growth of thick, homogeneous layers of Ga 1- x Al x As (ϰ ≤ 0.72) are reported. By application of the modified LPEE procedure proposed by Daniele and Heblig, we were able to grow from 4.4 g of Ga, at 800°C, a Ga 0.76 Al 0.24 As layer as thick as 330 μm. It was experimentally proven that this method results in thicker and more homogeneous layers than those grown by standard LPEE and LPE. The dependence of layer composition on the initial composition of the solution is experimentally obtained.