Abstract
This work deals with GaSb-based diode lasers grown by solid source molecular beam epitaxy and operating in high power continuous wave regime at room temperature in mid-infrared spectral region near and above 2 Μm. Firstly, we present experimental and theoretical studies of the effect of the compressive strain above 1% on differential gain and threshold current of GaSb-based type-I quantum well diode lasers on the example of 2.3 Μm emitters. The experimental results supported by theoretical calculations conclusively demonstrated that improvement of the hole confinement was primarily responsible for the observed enhancement of the optical gain and the reduction of the threshold current density in laser structures with heavily strained QWs. Secondly, we introduce quinary AlGaInAsSb as waveguide/barrier material to improve hole confinement in 2.7 Μm emitters. Room temperature continuous wave output power of 600 mW was demonstrated for emitters with 470-nm-wide AlGaInAsSb waveguide optimized for improved device differential gain. Thirdly we describe the design approach and demonstrate the experimental results for 2 Μm emitting high power devices with reduced fast axis beam divergence in far field. When asymmetric cladding and non-broadened waveguide design were employed, the fast axis far field beam divergence was reduced from 62° to 37° while keeping favorable threshold current density and internal efficiency. Finally, we fabricate and characterize single spatial mode room temperature operated 3.15 Μm diode lasers. Ridge waveguide lasers generate 9 mW of continuous wave output power in a diffraction limited beam at 20°C.
