Abstract
Lightly doped n-type GaSb substrates with p-type GaSb buffer layers are the preferred templates for growth of InAs/InGaSb superlattices used in infrared detector applications because of relatively high infrared transmission and a close lattice match to the superlattices. We report here temperature dependent resistivity and Hall effect measurements of bare substrates and substrate-p-type buffer layer structures grown by molecular beam epitaxy. Multicarrier analysis of the resistivity and Hall coefficient data demonstrate that high temperature transport in the substrates is due to conduction in both the high mobility zone center Γ band and the low mobility off-center L band. High overall mobility values indicate the absence of close compensation and that improved infrared and transport properties were achieved by a reduction in intrinsic acceptor concentration. Standard transport measurements of the undoped buffer layers show p-type conduction up to 300 K indicating electrical isolation of the buffer layer from the lightly n-type GaSb substrate. However, the highest temperature data indicate the early stages of the expected p to n type conversion which leads to apparent anomalously high carrier concentrations and lower than expected mobilities. Data at 77 K indicate very high quality buffer layers.
Highlights
There is continued interest in type-II InAs/GaSb and InAs/InGaSb superlattices (SL) because of their important applications as infrared detectors.[1,2,3] The SL material with the best structural quality is grown on GaSb substrates where lattice mismatch induced dislocations are at a minimum
Doped n-type GaSb substrates with p-type GaSb buffer layers are the preferred templates for growth of InAs/InGaSb superlattices used in infrared detector applications because of relatively high infrared transmission and a close lattice match to the superlattices
We report here a study of the electrical properties of highly transmitting, lightly doped n-type GaSb substrates and of undoped p-type GaSb buffer layers grown on those substrates
Summary
There is continued interest in type-II InAs/GaSb and InAs/InGaSb superlattices (SL) because of their important applications as infrared detectors.[1,2,3] The SL material with the best structural quality is grown on GaSb substrates where lattice mismatch induced dislocations are at a minimum. Semi-insulating GaAs and InP substrates are transparent at wavelengths of interest but have large lattice mismatch Both undoped p-type GaSb substrates and standard heavily Te doped n-type GaSb substrates, (p GaSb and n+ GaSb respectively) have strong absorption in the mid and long wavelength infrared regions (MWIR and LWIR). This absorption is usually attributed to free carrier absorption. We report here a study of the electrical properties of highly transmitting, lightly doped n-type GaSb substrates and of undoped p-type GaSb buffer layers grown on those substrates
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