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4 Acta Physica Polonica A

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Photoconductivity in GaAlAs:Si Proves Negative U of DX Centers

100%

Wilamowski Z. , Jantsch W. , Ostermayer G.

Acta Physica Polonica A

1991

tom 80

nr 2

283-286

The analysis of the temperature dependence of the photoconductivity, amplitude in doped GaAlAs, provides a simple and convincing proof of the negative sign of the Hubbard correlation energy U, strictly speaking of the two-electron nature of the thermal emission process from DX centers. The proof is based on a comparison of the emission activation energy measured per emission event (DLTS) with that measured per electron.

Consequences of Spatial Fluctuation of Coulomb Potential in AlGaAs with DX Centers

100%

Wilamowski Z. , Kossut J. , Jantsch W. , Ostermayer G.

Acta Physica Polonica A

1991

tom 80

nr 3

385-388

Electric charges on randomly distributed impurities in semiconductors produce a spatially fluctuating potential. When the impurities are partially filled, their occupancy is not random but there appears a spatial correlation of the impurity charges appearing due to the inter-impurity Coulomb interactions. We show that when these interactions are taken into account then (i) the activation energy of the electron concentration, (ii) thermal emission kinetics, (iii) capture kinetics, (iv) persistent photoconductivity kinetics and (v) the electron mobility (in a steady state as well as during transients) in GaAlAs:Si can be explained in a consistent way. The energy diagram con cerning the DX center levels with respect to minima of the conduction band as well as the capture and emission barriers (including the effect of the alloy splitting) is constructed within an approach making use of the notion of the impurity self-screening.

Alloy Splitting of the Te-DX States in Al_{x}Ga_{1-x}As

88%

Ostermayer G. , Jantsch W. , Dobosz D. , Żytkiewicz Z. , Wilamowski Z.

Acta Physica Polonica A

1993

tom 84

nr 4

769-772

We report investigations of the Hall effect and conductivity of Te doped Al_{x}Ga_{1-x}As (x = 0.3). After illumination at low temperature, the conductivity decreases in two steps on warming. These steps are explained in terms of the two sets of energy levels associated with two types of Te-DX centers depending on the neighboring host cation (Ga or Al) which undergoes the 1attice relaxation. The observed persistent increase in mobility is also explained in terms of the two different capture barriers.

35×4 Substates of DX Centers in AlGaAs:Si

88%

Ostermayer G. , Brunthaler G. , Stöger G. , Jantsch W. , Wilamowski Z.

Acta Physica Polonica A

1993

tom 84

nr 4

765-768

The measured temperature dependent free carrier concentration in AlGaAs:Si samples is compared with a model calculation where we take the full 35 × 4 alloy statistics of the DX center and potential fluctuations into account. Within this statistics we are able to describe the electron capture by a single barrier E_{B} for all Al-configurations. We compare the alloy statistics with the simple 4 × 1 statistics.