Devices and desires in the 2-4 mu m region based on antimony-containing III-V heterostructures grown by MOVPE
The growth, by MOVPE, of a range of antimonide-based material systems suitable for providing devices responsive to 2-4 mu m wavelength radiation is reported. Photodetectors with external quantum efficiencies of 60% at 2.2 mu m have been fabricated from an InGaSb homojunction. In order to examine the possibility of tuning the wavelength of emission or detection by using a strained single quantum well (SSQW) of InGaSb/GaSb this has been grown in the depletion region of a GaSb homojunction. These novel heterostructures have been grown to produce devices without the need for conventional doping. Using the crossed-gap alignment of InAs/GaSb the authors can form a diode-like structure. The most promising devices have a turn-on voltage VTO of 0.7 V (1mA), and a typical reverse voltage VR=-12 V (0.1 mA) and a best VR of -12 V (10 mu A) for a 100 mu m diameter device with some evidence of avalanche breakdown in the structure. Abrupt doping junctions have been formed between GaSb and GaAs:Si substrates. The mismatch between the layers is ameliorated by using a low-temperature buffer layer to improve the interface. Avalanche breakdown starts at -4.5 V in these structures and reverse bias currents of <10 mu A at up to 2 V from unintentionally doped GaSb (uGaSb) with a carrier concentration of 1016 cm-3 p. Schottky barriers are an alternative to p/n junctions, but they cannot be made at all on uGaSb because of the low barrier height, which is of the order of 0.2 eV. We have overcome this problem using a thin capping layer of highly dislocated GaAs. Surprisingly this has been successful for both regrowth on older structures and contiguous in situ growth.