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Title:Zero-field time-of-flight characterization of minority carrier transport in heavily carbon-doped gallium arsenide and indium gallium arsenide
Author(s):Colomb, Carolyn Marie
Doctoral Committee Chair(s):Stillman, Gregory E.
Department / Program:Electrical and Computer Engineering
Discipline:Electrical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Electronics and Electrical
Physics, Condensed Matter
Abstract:Heavily doped p-type GaAs is important for both optical and electronic devices, and recently carbon has become the preferred base dopant for AlGaAs/GaAs and InGaP/GaAs heterojunction bipolar transistors (HBTs) due to its high solubility and low diffusivity in GaAs. The low diffusivity of carbon, relative to that of Be and Zn, has been demonstrated to lead to improvements in the stability of the base dopant profile and in AlGaAs/GaAs HBT reliability. Minority carrier electron diffusion coefficients and lifetimes have been measured in heavily doped p-type GaAs and In$\sb{0.53}$G$\sb{0.47}$As using the zero-field time-of-flight (ZFTOF) technique in structures that simulate the base transport in HBTs. To extract lifetimes and diffusion coefficients from the data, an analytical solution to the minority carrier diffusion equation is found, and the voltage and time derivative of the voltage are calculated using the short-circuit photocurrent and an equivalent circuit model. The calculated curves are then fit to the experimental data by adjusting the carrier lifetime and diffusion coefficient.
The GaAs material studied included: C-doped GaAs grown by metalorganic chemical vapor deposition (MOCVD) using CCl$\sb4$ and TMAs as the carbon sources, C-doped GaAs grown by molecular beam epitaxy (MBE) using CBr$\sb4$ and graphite as the carbon sources, and Be-doped GaAs grown by MBE. The hole concentration of the GaAs material ranged from 10$\sp{18}$ to 10$\sp{20}$ cm$\sp{-3}.$ Room temperature photoluminescence intensity measurements were made on some of the GaAs material and compared with ZFTOF measurements of lifetime. The C-doped material (p $\sim$ 10$\sp{19}$ cm$\sp{-3})$ which used graphite as the carbon source exhibited diffusion lengths of less than 1000 A. MOCVD-grown C-doped GaAs, which was optimized by adjusting the growth conditions to maximize the room temperature photoluminescence intensity, had diffusion lengths comparable to those measured in Be-doped GaAs for hole concentrations of $1\times10\sp{19}$ and $5\times10\sp{19}$ cm$\sp{-3}.$ Comparison of photoluminescence intensities also suggests that the addition of In to very heavily doped MOCVD-grown GaAs (p $>10\sp{20}$ cm$\sp{-3}$) to eliminate the lattice mismatch with respect to the substrate does not result in an improvement in lifetime.
The InGaAs material studied included: C-doped InGaAs grown by MOCVD using CCl$\sb4$ as the carbon source and Be-doped InGaAs grown by gas source MBE (GSMBE). The hole concentration of the InGaAs material ranged from 10$\sp{18}$ to $1.2\times10\sp{19}$ cm$\sp{-3}.$ The C-doped InGaAs with a hole concentration of $1.2\times10\sp{19}$ cm$\sp{-3}$ had a diffusion length of 6000 A.
Issue Date:1993
Rights Information:Copyright 1993 Colomb, Carolyn Marie
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9329004
OCLC Identifier:(UMI)AAI9329004

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