Evolution of planar defects during homoepitaxial growth of β-Ga2O3 layers on (100) substrates—A quantitative model

R Schewski,K Irmscher,B Neuschulz,Z Galazka,T Schulz,T Remmele,M Albrecht,M Baldini,A Fiedler,G Wagner,T Markurt

doi:10.1063/1.4971957

Abstract

We study the homoepitaxial growth of β-Ga2O3 (100) grown by metal-organic vapour phase as dependent on miscut-angle vs. the c direction. Atomic force microscopy of layers grown on substrates with miscut-angles smaller than 2° reveals the growth proceeding through nucleation and growth of two-dimensional islands. With increasing miscut-angle, step meandering and finally step flow growth take place. While step-flow growth results in layers with high crystalline perfection, independent nucleation of two-dimensional islands causes double positioning on the (100) plane, resulting in twin lamellae and stacking mismatch boundaries. Applying nucleation theory in the mean field approach for vicinal surfaces, we can fit experimentally found values for the density of twin lamellae in epitaxial layers as dependent on the miscut-angle. The model yields a diffusion coefficient for Ga adatoms of D = 7 × 10−9 cm2 s−1 at a growth temperature of 850 °C, two orders of magnitude lower than the values published for GaAs.

Highlights

Monoclinic Ga2O3 (b-Ga2O3) is a semiconductor with a bandgap of 4.7 eV and an estimated break down field of 8 MVcmÀ1.1 It has recently attracted considerable interest as a promising material for applications such as solar blind UV photo detectors2,3 and high power devices.4,5 Epitaxial growth of structurally perfect crystalline layers with defined doping is a prerequisite to fully use its potential for device applications
We have shown that homoepitaxial growth by metal organic vapor phase epitaxy (MOVPE) on (100) b-Ga2O3 is challenging since stacking faults in form of twin lamella are present in epitaxial layers
Formation of these twin lamellae is a result of double positioning of 2D islands on the b-Ga2O3 (100) plane

Summary

Introduction

Monoclinic Ga2O3 (b-Ga2O3) is a semiconductor with a bandgap of 4.7 eV and an estimated break down field of 8 MVcmÀ1.1 It has recently attracted considerable interest as a promising material for applications such as solar blind UV photo detectors and high power devices. Epitaxial growth of structurally perfect crystalline layers with defined doping is a prerequisite to fully use its potential for device applications. Formation of stacking faults and twin lamellae has been studied in early work on epitaxial growth of face centered cubic metals by Hall and Thompson, and Dickson and Pashley.19 Their models, later adopted for other material systems and crystal symmetries (e.g., SiC, CdTe21), start from the assumption that growth on surface facets proceeds through nucleation and growth of two-dimensional islands. Formation of twin lamellae through double positioning is inhibited, if growth takes place in the step flow mode This is promoted if at a given growth temperature the surface diffusion length of the adatoms is higher than the typical width of surface terraces, i.e. in this case adatoms will be able to reach the nearest step edge. Despite this qualitative understanding and pragmatic solutions, a quantitative model that describes twin lamella formation through double positioning has not been presented yet

Results

Discussion

Conclusion