Majority-Carrier Mobilities in Undoped and \textit{n}-type Doped ZnO Epitaxial Layers

TL;DR

This study investigates the electron mobility in undoped and n-type doped ZnO epitaxial layers, revealing unusual mobility behavior at certain carrier concentrations and analyzing scattering mechanisms affecting mobility.

Contribution

It provides new insights into the mobility behavior in ZnO layers and compares experimental data with theoretical models to explain scattering effects.

Findings

Mobility peaks at certain carrier concentrations and then decreases.

Ionized donors and oxygen traps influence mobility.

Theoretical models align with experimental observations.

Abstract

Transparent and conductive ZnO:Ga thin films are prepared by laser molecular-beam epitaxy. Their electron properties were investigated by the temperature-dependent Hall-effect technique. The 300-K carrier concentration and mobility were about $n_s \sim 10^{16}$ cm$^{-3}$ and 440 cm$^{2}$/Vs, respectively. In the experimental `mobility vs concentration' curve, unusual phenomenon was observed, i.e., mobilities at $n_s \sim 5\times$ 10$^{18}$ cm$^{-3}$ are significantly smaller than those at higher densities above $\sim 10^{20}$ cm$^{-3}$. Several types of scattering centers including ionized donors and oxygen traps are considered to account for the observed dependence of the Hall mobility on carrier concentration. The scattering mechanism is explained in terms of inter-grain potential barriers and charged impurities. A comparison between theoretical results and experimental data is made.