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Congratulations to Dr. Vinita Rogers on the successful defense of her dissertation!

Congratulations to Dr. Vinita Rogers on a successful defense of her "Investigation of Antimonide based Metamorphic Buffers and Detectors" dissertation!

The abstract can be viewed below.

Abstract:

There is continued demand for the development of large area format focal plane arrays for higher throughput without compromising the device performance. This has led to a significant research and development thrust to utilize the commercially available large area substrates such as Silicon and GaAs. However, the lattice-mismatch heteroepitaxy leads to threading dislocations (TDs) which affect the minority carrier devices. As such, for a decade much attention was directed towards the 6.1 Å strained layer superlattice III-V semiconductors in the mid-wave IR (MWIR) and long-wave IR (LWIR) region, which can be grown pseudo morphically on lattice-matched GaSb substrates and lattice-mismatch heteroepitaxy is highly neglected in the III-Sb based IR detector community.  Recently, application of strain relieving buffer approach revealed that the bulk InAs1‑ySby has significantly large bowing parameter which gives the smallest bandgap among III-V compound semiconductors. The discovery of the large bowing parameter in bulk InAs1-ySby alloy is of significant interest especially in the LWIR detection range, since theoretically, bulk InAs1-ySby has absorption coefficient similar to the incumbent HgCdTe detectors which are currently ruling the MWIR-LWIR detectors market and suffers from low yield and compositional non-uniformity.

The research efforts in the lattice-mismatch heteroepitaxial bulk InAs1-ySby detectors are in the early stages of development and significant effort is required in the maturation of the high-quality, low threading dislocation density (TDD) metamorphic buffers for LWIR InAs1-ySby alloys and understand the dominant mechanisms of dark current in lattice-match versus mismatch substrates for MWIR InAs1-ySby .

This work is focused towards the development of low TDD metamorphic buffers using Al1‑xInxSb and InAs1‑ySby using molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) respectively. The preliminary MBE and MOCVD metamorphic grade results shows that TDD as low as of the order of 106 per cm2 can be obtained and might be the promising candidate in the near future.

Final efforts are made to analyze the dark current of the MBE grown MWIR InAs1‑ySby nBn detector grown on lattice match (GaSb) versus mismatch (GaAs and Si) substrates to unravel the effect of TDs. Dark current modeling was done to fit the measured dark current data to determine the key contributors of dark current in the three samples. TDs reduced the minority carrier lifetime and led to higher generation-recombination current. MWIR InAs1‑ySby is less prone to TDs in the low bias region. However, in the high reverse bias, tunneling current starts to dominate in the detectors grown on mismatch samples. Although, from the detector’s operation perspective, only lower bias region is significant where effect of TD is minimal in MWIR InAs1‑ySby paving path forward to the mismatch substrates. This indicates that growth of metamorphic antimonide detectors on Silicon and GaAs is a potentially path forward for large area focal plane arrays.

 

Vinita is the first Ph.D. graduate out of the KIND group since coming to Ohio State.