Band-tail shape and transport near the metal-insulator transition in Si-doped Al(0.3)Ga(0.7)As

TL;DR

This study investigates the transport properties and band-tail shape near the metal-insulator transition in Si-doped AlGaAs using in situ photodoping and transport measurements, revealing an exponential density of states and a critical carrier concentration for MIT.

Contribution

It introduces a method to vary electron density in Si-doped AlGaAs in situ and characterizes the band-tail shape and MIT behavior through transport measurements.

Findings

MIT occurs at 5.7x10^16 cm^-3 for S1 at 350 mK

Band-tail density of states is exponential with exponents -1.25 and -1.38

Mobility is limited by ionized impurity scattering and fits Brooks-Herring theory

Abstract

In the present work, an infrared LED is used to photodope MBE-grown Si:Al(0.3)Ga(0.7)As, a well known persistent photoconductor, to vary the effective electron concentration of samples in situ. Using this technique, we examine the transport properties of two samples containing different nominal doping concentrations of Si (1x10^19 cm^-3 for sample 1 (S1) and 9x10^17 cm^-3 for sample 2 (S2)) and vary the effective electron density between 10^14 and 10^18 cm^-3. The metal-insulator transition (MIT) for S1 is found to occur at a critical carrier concentration of 5.7x10^16 cm^-3 at 350 mK. The mobilities in both samples are found to be limited by ionized impurity scattering in the temperature range probed, and are adequately described by the Brooks-Herring screening theory for higher carrier densities. The shape of the band-tail of the density of states (DOS) in Al(0.3)Ga(0.7)As is found electrically through transport measurements. It is determined to be exponential in character, with an exponent of -1.25 for S1 and -1.38 for S2.