GROWTH OF GASB ON GAAS SUBSTRATES

The initial growth of GaSb on GaAs substrates by atmospheric pressure metalorganic vapour phase epitaxy (MOVPE) has been investigated both i n-situ and ex-situ. The in-situ technique used was quasi-elastic light scattering (QLS) and the ex-situ technique was atomic force microscop y (AFM) measurements. Both techniques show that there is a narrow rang e of III:V ratios where good island nucleation can be achieved. Both t echniques also show that the islands grow anisotropically along the [1 10] directions. At low growth temperatures (less than or similar to 52 0 degrees C) they are longer along the [110] direction; at similar to 540 degrees C they are nearly square, and at high growth temperatures (greater than or similar to 560 degrees C) they are longer along the [ ($) over bar 110] direction. The size, shape and number density of the islands depend on the III:V ratio, growth time, growth rate and growt h temperature. At low growth temperatures and growth rates it has not been possible to observe full coalescence of small islands using the u sual trimethyl alkyls, so triethylgallium (TEGa) and tertiarybutlydime thylantimony (tBDMSb) have been used instead. These have much better p yrolysis characteristics (25% pyrolysed at 520 degrees C compared with 5%) and give much more efficient growth. This combination has allowed full coalescence of small islands grown at 520 degrees C for the firs t time. The improvements achieved in the morphology of thick layers of GaSb on GaAs have allowed us to fabricate a novel InAs/GaSb ballistic transport device.