Comparison of Thermal and Atomic-Hydrogen-Assisted Oxide Desorption Methods for Regrowth of GaSb-Based Cascade Diode Lasers

Abstract

Epitaxial regrowth of antimonide-based heterostructures is required either to improve device performance parameters or to achieve new functionalities. This work compares two major methods used for surface preparation for subsequent epitaxial regrowth in the context of antimonide heterostructures. An advantage of the atomic-hydrogen-assisted oxide removal process for regrowth of GaSb-based type I quantum well cascade diode lasers is demonstrated experimentally. Wide-ridge 2.7-µm cascade diode lasers have been fabricated from heterostructures grown either in a single epitaxial run (benchmark) or in two separate epitaxial steps (regrowth test). The heterostructure used in regrowth experiment was initially grown only up to the top waveguide layer comprising 500 nm of lightly p-doped GaSb. The surface of this incomplete laser heterostructure was exposed to typical hard mask formation and removal processing treatments. Then, the surface was chemically cleaned and subjected to two different oxide desorption methods prior to regrowth of the top cladding layer. The high-temperature thermal oxide desorption and low-temperature atomic-hydrogen-based processes were tested. The devices based on laser heterostructures regrown with the utilization of the thermal oxide desorption step demonstrated nearly twofold higher laser threshold current densities and a significant reduction of slope efficiencies compared with reference lasers grown in a single growth run. The regrown lasers based on the atomic-hydrogen-assisted surface preparation method demonstrated almost no degradation of parameters compared with the benchmark lasers. Atomic force microscopy studies of the GaSb epitaxial surface subjected to thermal oxide desorption demonstrated significant degradation of the surface morphology, while the GaSb surface cleaned by atomic hydrogen showed well-resolved atomic terraces.