IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Semiconductors Monday Sessions
       Session SC-MoM

Paper SC-MoM4
Measurement of Charge Separation Potentials In GaAs(1-x)N(x)

Monday, October 29, 2001, 10:40 am, Room 124

Session: Band-Engineered Electronic Materials
Presenter: S.W. Johnston, National Renewable Energy Laboratory
Authors: S.W. Johnston, National Renewable Energy Laboratory
R.K. Ahrenkiel, National Renewable Energy Laboratory
C.W. Tu, University of California, San Diego
Y.G. Hong, University of California, San Diego
Correspondent: Click to Email
The ternary alloy GaAs(1-x)N(x) is interesting as a semiconductor that can be grown epitaxially on GaAs. As is well known, the bandgap can be reduced by as much as 0.4 eV by changing the nitrogen concentration from 0% to 3%. We measured the spectral response and photoconductive lifetime of the alloys, as a function of temperature. In this work, the films were grown by gas-source molecular beam epitaxy on semi-insulating GaAs substrates. All measurements were made using the contactless, resonant-coupled photoconductive decay (RCPCD) method. Our data shows that the spectral or excitation spectra of GaAs1-xNx alloys consists of photoconductive band tails that extend well into the infrared (beyond the nominal bandgap). For example, the photoconductive bandtails extend to about 1.8 mm for GaAs(0.97)N(0.03). The primary photoconductive decay times are in the range of 200 to 300 ns. At temperatures below about 200 K, the decay rate begins to decrease with lowered temperature. By plotting the inverse lifetime versus 1/T, one generates the standard Arrhenius plot of a thermally activated process. These data fits produce activation energies that increase with the N-content. The activation energies, DE, for compositions x = 0.011, 0.023, and 0.033 are 67, 72, and 83 meV, respectively. These energies represent the potential barriers which inhibit recombination. The increase of DE with x is indicative of charge separation being related to N-atom clustering. Our model suggests that these barriers originate from the inhomogenous band structure produced by the random distribution of the nitrogen impurity.