Type-II InAs/InGaSb Superlattices on Compliant GaAs Substrates
- PDF / 1,485,726 Bytes
- 6 Pages / 415.8 x 637.2 pts Page_size
- 30 Downloads / 223 Views
ABSTRACT Type-II InAs/GaInSb superlattices of different designs have been grown by molecular beam epitaxy on wafer bonded InGaAs on GaAs, and on standard GaSb substrates. The extremely thin (-100A) InGaAs layer is loosely bonded to the GaAs substrate and serves as a compliant layer for subsequent epitaxy of a larger lattice constant material. The effects of these substrates on the optical, electrical, and structural properties of the superlattice were studied. The superlattices grown on bonded substrates were found to have uniform layers, with broader x-ray linewidths than superlattices grown on GaSb. The photoresponse results for the superlattices on the bonded 2 inch diameter substrates, with the InGaAs compliant layer, were not as favorable as early work on similar, smaller area, bonded substrates. However, refinements to the wafer bonding process to eliminate microvoids between the bonded layers will provide higher quality superlattices. INTRODUCTION Type-Il superlattices of InAs/InxGalxSb are potentially a III-V, intrinsic alternative to HgxCdl-,Te alloys for infrared detector arrays.'14 The band gap of these superlattices (SLs) can be continuously adjusted by changing the composition and thickness of the layers to cover the mid- to very long wavelength infrared spectrum. The InAs/lnxGal-,Sb type-II SLs have infrared absorption coefficients comparable to HgxCdl_•Te alloys and have the potential for higher temperature operation due to Auger recombination suppression.' 6 The disadvantages to these superlattices for IR detection is the sensitivity of the band gap to small design changes and the fact that the carrier lifetimes are currently Shockley-Read Hall limited due to defects instead of Auger limited. Another potential issue in the development of infrared imaging arrays utilizing type-II InAs/InGaSb superlattices is the GaSb substrates used for lattice-matched epitaxial growth. These substrates are conductive, limited to two inch diameters, and are highly absorbing at infrared wavelengths greater than 5 micrometers. A possible alternative to the GaSb substrates is the use of GaAs or silicon substrates. The IR transmission of both GaAs and silicon is much higher than GaSb, for the same wafer thickness. GaAs is nearly flat out to 17.6 gtm, where phonon absorption begins to dominate, and silicon has good transmission beyond 18 pom (see Fig. 1). Unfortunately both of these substrates have a substantial difference in lattice constant compared to InAs/lnGaSb superlattices (> 6. 1A). Attempts have been made to grow high quality superlattices on GaAs substrates with thick GaSb buffer layers. 7-9 However, the use of GaAs substrates has been mostly abandoned because higher crystalline quality superlattices were 0 always grown on GaSb substrates.' Instead of trying more and more complex buffer layer designs, an unconventional solution to growing the superlattice layers on GaAs is to employ the concept of a thin, loosely bonded, or compliant, layer as the intermediary. Early exploratory work on thin, twist-bonded layers
Data Loading...
