The 6.1 Å family (InAs, GaSb, AlSb) and its heterostructures: a selective review

The three semiconductors InAs, GaSb, and AlSb form an approximately lattice-matched set around 6.1 Å, covering a wide range of energy gaps and other properties. Of particular interest are heterostructures combining InAs with one or both of the antimonides, and they are emphasized in this review. In addition to their use in conventional device types (FETs, RTDs, etc.), several heterostructure configurations with unique properties have been explored, especially InAs/AlSb quantum wells and InAs/GaSb superlattices. InAs/AlSb quantum wells are an ideal medium to study the low-temperature transport properties in InAs itself. With gate-induced electron sheet concentrations on the order 10 ¹² cm^-2, they exhibit a pronounced conductivity quantization. The very deep wells (1.35 eV) provide excellent electron confinement, and also permit modulation doping up to at least 10 ¹³ electrons cm^-2. Because of the very low effective mass in InAs, heavily doped wells are essentially metals, with Fermi energies around 200 meV, and Fermi velocities exceeding 10 ⁸ cm s ^-1. Contacted with superconducting electrodes, such structures can act as superconductive weak links. InAs/GaSb-related superlattices with their broken-gap lineup behave like semimetals at large lattice periods, but if the lattice period is shortened, increasing quantization effects cause a transition to a narrow-gap semiconductor, making such structures of interest for infrared detectors, often combined with the deliberate addition of strain.