Tailoring the electrical properties of Ge/GaAs by film deposition rate and preparation of fully compensated Ge films

Abstract

We investigate the electronic, optical, and structural properties of thin Ge/GaAs(100) films for a variety of growth rates. All of the films have a granular, single-crystal structure, but the electronic properties vary dramatically, with resistivity and carrier concentration changing by more than three orders of magnitude. For high deposition rates, the films are heavily doped and of n-type, with relatively high carrier concentration and low resistivity. The temperature dependence of the resistivity indicates metalliclike transport with degenerate charge carriers. For low deposition rates, the films are p-type, with lower carrier concentrations and higher resistivity whose temperature dependence indicates semiconducting, activation-type transport with an activation energy that can reach up to half of the Ge band gap. Such films are heavily doped and strongly (sometimes fully) compensated Ge. At moderate deposition rates, a metal-insulator transition occurs. The electrical properties of strongly compensated Ge films are analyzed in terms of the two-dimensional percolation of charge carriers through a fluctuating electrostatic potential.

Transition between Efros–Shklovskii and Mott variable-range hopping conduction in polycrystalline germanium thin films

“…However, a number of results which deviated from the VRH predictions remain in existence. In addition, the growth conditions [11], impurity doping [12] and crystallization states [13,14] of germanium films also impact their electrical properties. Therefore, it is necessary to carry out more experimental and theoretical research on the electron transport of germanium films.…”

Structural study of Ge/GaAs thin films

“…The high deposition rates produce films that are n-type doped with low resistivity (10 -2 cm) and high carrier concentration (410 18 cm 3 ). The temperature dependence of conductivity in these films is very weak and of non-activation [10]. In this work we present a structural study of thermally deposited Ge/GaAs films by transmission electron microscopy (TEM) and atomic force microscopy (AFM).…”

“…However, the effect of the deposition rate on the properties of thin Ge films on GaAs has not been investigated thoroughly; in most of the reports rather high film deposition rates have been chosen as a rule. Recently we have demonstrated that by varying the deposition rate of Ge/GaAs one can control the transport properties effectively [10]. The high deposition rates produce films that are n-type doped with low resistivity (10 -2 cm) and high carrier concentration (410 18 cm 3 ).…”