Minority carrier diffusivity measurements in III-V semiconductors by the zero-field time-of-flight technique

Michael Lowell Lovejoy, Purdue University

Abstract

Minority carrier diffusivity, or equivalently mobility, is an important transport parameter that determines the performance of devices such as transistors and solar cells. Heavily doped gallium arsenide (GaAs) is an important material system for these devices, however, minority carrier diffusivity data are lacking because the diffusivity is difficult to measure. A major objective of this study was to critically analyze the zero-field time-of-flight (ZFTOF) technique and to develop application criteria for measuring the minority carrier diffusivity in heavily doped III-V semiconductors. The main objective of this project was to measure the doping dependence of minority diffusivity in heavily doped n- and p-type GaAs and to compare minority electron properties for Be- and C-doped p$\sp+$-GaAs. Both minority hole and electron diffusivities were found to be higher than theoretically predicted, and the minority electron mobility was higher than was deduced from high-field measurements. Furthermore, the electron properties were found to be the same for p$\sp+$-GaAs doped to $\sim$10$\sp{19}$ cm$\sp{-3}$ with beryllium and with carbon. The higher than expected diffusivities were shown to have important implications on device performance. The final objective was to extend the ZFTOF technique to temperature-dependent minority diffusivity measurements. To that end, a ZFTOF cryogenic system was designed and built. The system was being tested at the time this is being written. It is anticipated that temperature-dependent measurements with the new cryostat will provide data which will help to identify the important scattering mechanisms that limit the performance of bipolar devices.

Degree

Ph.D.

Advisors

Melloch, Purdue University.

Subject Area

Electrical engineering|Condensation|Electromagnetism

COinS