The performance and operating temperature of infrared (IR) detectors is largely limited by thermal generation and noise processes in the active region of the device. Particularly, excess background charge carriers enhance Auger recombination and dark currents, and depress the detector figures of merit. Therefore, reducing background carriers in the undoped region of pin diodes is an important issue for developing high-operating temperature IR detectors. In this paper, we discuss how, through low-temperature Hall measurements, we optimized several growth and design parameters to lower residual carrier densities in various mid-IR InAs/GaSb superlattice (SL) designs. Among the growth/processing parameters investigated in the 21 Å InAs/24 Å GaSb SLs, neither growth temperature nor in-situ post-growth annealing significantly affected the overall carrier type and density. All of the mid-IR SL samples investigated were residually p-type. The lowest carrier density (1.8x10¹¹ cm^-2) was achieved in SLs grown at 400 °C and the density was not reduced any further by a post-growth anneal. The growth parameter that most affected the carrier density was interface composition control. With a minor variation in interface shutter sequence, the carrier density dramatically increased from ~2x10¹¹ to 5x10¹² cm^-2, and the corresponding mobility dropped from 6600 to 26 cm²/Vs, indicating a degradation of interface quality. However, the carrier density was further reduced to 1x10¹¹ cm^-2 by increasing the GaSb layer width. More importantly, a dramatic improvement on the photoluminescence intensity was achieved with wider GaSb SLs. The disadvantage is that as GaSb layer width increases from 24 to 48 Å, the photoluminescence peak position shifts from 4.1 to 3.4 μm, for a fixed InAs width of 21 Å, indicating a photodiode based on these wider designs would fall short of fully covering the 3 to 5 μm mid-IR spectral region.

Date Published: 26 January 2009
PDF: 9 pages
Proc. SPIE 7222, Quantum Sensing and Nanophotonic Devices VI, 72220Y (26 January 2009); doi: 10.1117/12.810520

Published in SPIE Proceedings Vol. 7222:
Quantum Sensing and Nanophotonic Devices VI
Manijeh Razeghi; Rengarajan Sudharsanan; Gail J. Brown, Editor(s)