Investigation of Surface Passivation in InAs/GaSb Strained-Layer-Superlattices Using Picosecond Excitation Correlation M
- PDF / 108,558 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 59 Downloads / 191 Views
0891-EE01-08.1
Investigation of Surface Passivation in InAs/GaSb Strained-Layer-Superlattices Using Picosecond Excitation Correlation Measurement and Variable-Area Diode Array Surface Recombination Velocity Measurement Zhimei Zhu, 1Elena Plis, 1Abdenour Amtout, Pallab Bhattacharya, and 1Sanjay Krishna Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109, U. S. A. 1 Center for High Technology Materials, University of New Mexico, Albuquerque, NM 87106, U. S. A.
ABSTRACT The effect of ammonium sulfide passivation on InAs/GaSb superlattice infrared detectors was investigated using two techniques, namely, picosecond excitation correlation (PEC) measurement and variable-area diode array (VADA) surface recombination velocity (SRV) measurement. PEC measurements were conducted on etched InAs/GaSb superlattice mesas, which were passivated in aqueous ammonium sulfide solutions of various strengths for several durations. The PEC signal’s decay time constant (DTC) is proportional to carrier lifetimes. At 77 K the PEC signal’s DTC of the as-grown InAs/GaSb superlattice sample was 2.0 ns, while that of the unpassivated etched sample was reduced to 1.2 ns by the surface states at the mesa sidewalls. The most effective ammonium sulfide passivation process increased the PEC signal’s DTC to 10.4 ns. Using the best ammonium sulfide passivation solution found in PEC experiments, a VADA SRV measurement was undertaken to compare SRVs in unpassivated and passivated diodes. The obtained SRV in the depletion region of the InAs/GaSb superlattice and GaSb junction was 1.1×106 cm/s for the unpassivated sample and 4.6×105 cm/s for the passivated sample. At 77 K the highest R0A value measured in our passivated devices was 2540 Ω cm2 versus 0.22 Ω cm2 for the unpassivated diodes. The results of the lifetime, the SRV and the R0A measurements indicate that ammonium sulfide passivation will improve the performance of InAs/GaSb superlattice infrared detectors. INTRODUCTION InAs/GaSb type-II superlattices, which feature a staggered band alignment, have recently received significant attention as a promising material system for the fabrication of high performance infrared (IR) focal plane arrays. One major problem associated with mesa photodiode IR detectors based on InAs/GaSb superlattices is the dangling bonds at the surface of the etched sidewalls. These dangling bonds induce surface states that lead to surface generationrecombination (g-r) current, which becomes a more dominant dark current component, as the photodiodes are made smaller. This is especially true in focal plane arrays, where each pixel has an edge length of 20-30 µm. The surface states also assist the recombination of photogenerated carriers, thereby reducing minority carrier lifetime and decreasing a detector’s responsivity and detectivity. For the aforementioned reasons, passivating the surface of InAs/GaSb superlattices is a
0891-EE01-08.2
significant challenge. In this paper, we report the result of an aqueous ammonium sulfide
Data Loading...
