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 mum wavelength radiation is reported. Photodetectors with external quantum efficiencies of 60% at 2.2 mum 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 we can form a diode-like structure. The most promising devices have a turn-on voltage V(TO) of 0.7 V (1 mA), and a typical reverse voltage V(R) = - 12 V (0.1 mA) and a best V(R) of - 12 V (10 muA) for a 100 mum 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 muA at up to 2 V from unintentionally doped GaSb (uGaSb) with a carrier concentration of 10(16) 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 re-growth on older structures and contiguous in situ growth.