DEEP LEVELS IN SNTE-DOPED GASB GROWN ON GAAS BY MOLECULAR-BEAM EPITAXY

A dominant deep level with an activation energy of 0.23-0.26 eV was ob served by admittance spectroscopy in SnTe-doped GaSb layers grown dire ctly on GaAs substrates by molecular beam epitaxy (MBE). The Sb-4/Ga B ur ratio was found to affect the Hall mobility and the concentration o f the deep level in a similar way, with an optimal beam equivalent pre ssure ratio of around 7 obtained for GaSb grown at 550 degrees C, whic h should correspond to the lowest ratio at which a Sb-stabilized surfa ce reconstruction can be maintained. This electron level is commonly d etected in n-type (SnTe-, S- and Te-doped) GaSb, but not in undoped p- type GaSb, suggesting that the level is not a simple native defect, bu t may be connected with the impurity used for n-type doping of GaSb.