Antimonide research:

MIDWAVE INFRARED DEVICES:

The band gap of antimonide alloys covers a wide spectral range from 300nm to 4.3um.  From a device point of view, the antimonide alloys are attractive for mid-infrared optoelectronic applications because they have a large split-off energy that leads to a reduced Auger recombination rate.   Despite this attractiveness optoelectronic devices grown on GaSb are difficult to realize because the mixed arsenide – antimonide heterostructures that are required for many devices have a type-II band alignment (see inset on MBE homepage).



To create efficient devices using the type-II band alignment we have used designs from Dr. Jerry Meyer group at NRL for a “W” structure laser.  In a departure from other instances of this laser we have grown the devices of 0 alloys made from 8 elements (Al, Ga, In, As, and Sb with Si, Be, and Te dopants) using random alloy cladding layers instead of binary alloy layers.  Two key optimizations that were required for this structure to be realized was the calibration of a mixed arsenide-antimonide quaternary alloy, and the optimization of growth temperature of the active region.  With optimized growth conditions, the laser device shows strong peak around 3.5µm at low temperature and room temperature lasing with a threshold current density of 965 Acm-2.  The low temperature laser spectrum is shown in red.

METAMORPHIC GROWTH

There are often times when an alloy with an important bandgap cannot be realized on commonly available substrates such as GaAs, InP, or GaSb.  Other times, one may wish to mix material systems on a single platform.  Metamorphic growth describes the growth of a layer with a different lattice constant than that of the initial substrate. The lattice mismatches in the buffers are accommodated through the formation of dislocations. Key issues when growing metamorphic structures are to minimize the number of threading dislocations that penetrate through to the active region of the heterostructure, and to reduce the surface roughness caused by non-uniform growth on a strained surface.  We’ve demonstrated many metamorphic layers of antimonides on GaAs substrate, and InP grown on GaAs.