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Title: Suppression of compensating native defect formation during semiconductor processing via excess carriers

Abstract

In many semiconductors, compensating defects set doping limits, decrease carrier mobility, and reduce minority carrier lifetime thus limiting their utility in devices. Native defects are often responsible. Suppressing the concentrations of compensating defects during processing close to thermal equilibrium is difficult because formation enthalpies are lowered as the Fermi level moves towards the majority band edge. Excess carriers, introduced for example by photogeneration, modify the formation enthalpy of semiconductor defects and thus can be harnessed during crystal growth or annealing to suppress defect populations. Herein we develop a rigorous and general model for defect formation in the presence of steady-state excess carrier concentrations by combining the standard quasi-chemical formalism with a detailed-balance description that is applicable for any defect state in the bandgap. Considering the quasi-Fermi levels as chemical potentials, we demonstrate that increasing the minority carrier concentration increases the formation enthalpy for typical compensating centers, thus suppressing their formation. Furthermore, this effect is illustrated for the specific example of GaSb. While our treatment is generalized for excess carrier injection or generation in semiconductors by any means, we provide a set of guidelines for applying the concept in photoassisted physical vapor deposition.

Authors:
 [1];  [2]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. Univ. of Utah, Salt Lake City, UT (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1260143
Report Number(s):
NREL/JA-5K00-66494
Journal ID: ISSN 2045-2322
Grant/Contract Number:
AC36-08GO28308
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 6; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; semiconductors; defects; processing; electronic devices

Citation Formats

Alberi, Kirstin, and Scarpulla, M. A.. Suppression of compensating native defect formation during semiconductor processing via excess carriers. United States: N. p., 2016. Web. doi:10.1038/srep27954.
Alberi, Kirstin, & Scarpulla, M. A.. Suppression of compensating native defect formation during semiconductor processing via excess carriers. United States. doi:10.1038/srep27954.
Alberi, Kirstin, and Scarpulla, M. A.. 2016. "Suppression of compensating native defect formation during semiconductor processing via excess carriers". United States. doi:10.1038/srep27954. https://www.osti.gov/servlets/purl/1260143.
@article{osti_1260143,
title = {Suppression of compensating native defect formation during semiconductor processing via excess carriers},
author = {Alberi, Kirstin and Scarpulla, M. A.},
abstractNote = {In many semiconductors, compensating defects set doping limits, decrease carrier mobility, and reduce minority carrier lifetime thus limiting their utility in devices. Native defects are often responsible. Suppressing the concentrations of compensating defects during processing close to thermal equilibrium is difficult because formation enthalpies are lowered as the Fermi level moves towards the majority band edge. Excess carriers, introduced for example by photogeneration, modify the formation enthalpy of semiconductor defects and thus can be harnessed during crystal growth or annealing to suppress defect populations. Herein we develop a rigorous and general model for defect formation in the presence of steady-state excess carrier concentrations by combining the standard quasi-chemical formalism with a detailed-balance description that is applicable for any defect state in the bandgap. Considering the quasi-Fermi levels as chemical potentials, we demonstrate that increasing the minority carrier concentration increases the formation enthalpy for typical compensating centers, thus suppressing their formation. Furthermore, this effect is illustrated for the specific example of GaSb. While our treatment is generalized for excess carrier injection or generation in semiconductors by any means, we provide a set of guidelines for applying the concept in photoassisted physical vapor deposition.},
doi = {10.1038/srep27954},
journal = {Scientific Reports},
number = ,
volume = 6,
place = {United States},
year = 2016,
month = 6
}

Journal Article:
Free Publicly Available Full Text
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Citation Metrics:
Cited by: 4works
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  • The amphoteric native defect model of the Schottky barrier formation is used to analyze the Fermi level pinning at metal/semiconductor interfaces for submonolayer metal coverages. It is assumed that the energy required for defect generation is released in the process of surface back-relaxation. Model calculations for metal/GaAs interfaces show a weak dependence of the Fermi level pinning on the thickness of metal deposited at room temperature. This weak dependence indicates a strong dependence of the defect formation energy on the Fermi level, a unique feature of amphoteric native defects. This result is in very good agreement with experimental data. Itmore » is shown that a very distinct asymmetry in the Fermi level pinning on p- and n-type GaAs observed at liquid nitrogen temperatures can be understood in terms of much different recombination rates for amphoteric native defects in those two types of materials. Also, it is demonstrated that the Fermi level stabilization energy, a central concept of the amphoteric defect system, plays a fundamental role in other phenomena in semiconductors such as semiconductor/semiconductor heterointerface intermixing and saturation of free carrier concentration.« less
  • The formation of defects during the initial stages of native-oxide growth on the GaSb (001)-α(4 × 3) surface has been studied computationally using spin-unrestricted density functional theory. It is found that insertion into a Ga-Sb adatom dimer to form a peroxo Ga-O-O-Sb bridge is the most energetically favorable process with insertion into Ga-Sb back-bonds being somewhat less so. A Ga-O-O-Ga bridge between dimers is also favorable, but Sb-O-O-Sb bridges show little if any stability. In the course of analyzing molecular adsorption, a particularly reactive site has been identified that leads to O{sub 2} dissociation with little or no barrier. This process ismore » initiated in the vicinity of an Sb-Sb dimer in the terminating layer and leads to sub-surface Ga and Sb defect sites (i.e., coordinatively unsaturated atoms) and to strained Ga-Sb bonds that may be susceptible to further O{sub 2} attack. However, the defects formed in these reactions do not produce states in the gap.« less
  • An expression for the collection velocity S of excess minority carriers at metal-semiconductor contacts is derived analytically for both the Schottky barrier and the Ohmic contact. Short-circuit conditions are assumed, appropriate to the collection of optically generated minority carriers by Schottky barriers or Ohmic contacts in solar cells or photodetectors. This analysis is then applied to the calculation of S for the materials of primary interest in solar cells (Si, GaAs, and CdS). It is found that S increases with the minority-carrier mobility and with the doping concentration according to Sapprox...mu../sub p/ N/sup 1///sup 2//sub d/ (for the contact: metal--n-typemore » semiconductor), but is independent of the barrier height phi/sub b/ or diffusion potential V/sub d//sub o/, provided qV/sub d//sub o/approximately-greater-than few KT. This means that, for Ohmic contacts, S depends on whether the contact is achieved by using high N/sub d/ (for which Sapprox. =10/sup 9/ cm/s for Si cells) or by low phi/sub b/ but moderate N/sub d/ (Sapprox. =10/sup 7/ cm/s for Si cells). More generally, S varies between approx. =10/sup 6/ cm/s (for CdS cells, low N/sub d/) and approx. =10/sup 10/ cm/s (p-type GaAs cells, high N/sub d/). Also defined are the conditions under which the finite collection velocity at the contact limits the collected minority-carrier current. (AIP)« less
  • The amphoteric native defect model of the Schottky barrier formation is used to analyze the Fermi level pinning at metal/semiconductor interfaces for submonolayer metal coverages. It is assumed that the energy required for defect generation is released in the process of surface back-relaxation. Model calculations for metal/GaAs interfaces show a weak dependence of the Fermi level pinning on the thickness of metal deposited at room temperature. This weak dependence indicates a strong dependence of the defect formation energy on the Fermi level, a unique feature of amphoteric native defects. This result is in very good agreement with experimental data. Itmore » is shown that a very distinct asymmetry in the Fermi level pinning on p- and n-type GaAs observed at liquid nitrogen temperatures can be understood in terms of much different recombination rates for amphoteric native defects in those two types of materials. Also, it is demonstrated that the Fermi level stabilization energy, a central concept of the amphoteric defect system, plays a fundamental role in other phenomena in semiconductors such as semiconductor/semiconductor heterointerface intermixing and saturation of free carrier concentration. 33 refs., 6 figs.« less
  • This paper presents results on annealing of carrier-induced metastable defects in hydrogenated amorphous silicon ({ital a}-Si:H) and on the dependence of the defect kinetics on carrier density. The metastable defects were studied by measuring the threshold-voltage shifts on capacitors as a function of time, temperature, and bias. The defect generation and annealing exhibit stretched-exponential-like behavior where the characteristic time for defect generation is a function of carrier density. The ratio of carrier density to defects in equilibrium are determined to be approximately 0.1, the same ratio found in doped {ital a}-Si:H. The results are consistent with dispersive hydrogen motion throughmore » an exponential distribution of barrier heights. The hopping rate and the final-state energy depend on the carrier density. This dependence on carrier density explains the carrier-, light-, and doping-induced defect formation in {ital a}-Si:H. The increase of the hopping rate due to carriers accounts for the increase in the hydrogen-diffusion rate in doped material. While much of the data are consistent with a single-hop model, the lack of correlation between generation and annealing rates indicates that defect formation occurs by multiple hopping.« less