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The temperature dependence of the indirect bandgap in thallium bromide has been determined using variable temperature (5K to 300 K) cathodoluminescence. The spectra include transitions associated with both the indirect (2.66 eV at 5K) and the direct (3.0 eV at 5K) bandgaps. Leastsquares analysis has been used to obtain fitting parameters for three analytical models commonly applied to describe the dependence of the bandgap on temperature for the lowest energy indirect transition. The indirect bandgap emission shifts to an energy of 2.86 eV at 300 K. We find a significant difference in the behavior of the luminescence associated with the direct bandgap, which does not appear to shift to the extent predicted by earlier measurements of the exciton absorption edge. [ABSTRACT FROM AUTHOR]

The admittances and subthreshold characteristics of capacitors and MOSFETs on buried and surface In0.53Ga0.47As channel flatband wafers, with a dielectric of Al2O3 deposited on In0.53Ga0.47As, are reported. The admittance characteristics of both wafers indicate the presence of defect states within the oxide, in common with a number of other oxides on In0.53Ga0.47As. The two wafers studied have not been hydrogen annealed, but do show some similar features to FGA treated oxides on n+ substrates. We discuss how the possible presence of residual hydroxyl ions in as-grown Al2O3 may explain these similarities and also account for many of the changes in the properties of FGA treated n+ samples. The issues around the comparison of subthreshold swing (SS) results and the impact of transistor design parameters on the energy portion of the defect state distribution affecting efficient device switching are discussed. The interface state model is applied to low source-drain voltage SS data to extract an effective interface state density (Dit) that includes interface and oxide traps. The logarithmic gate voltage sweep rate dependence of the SS Dit is used to extract an oxide trap density (Dot) and a simple method is used to estimate the Fermi level position within the band gap, Et. The Al2O3 Dit(Et) and Dot(Et) distributions are found to be similar to each other and to the results of our analysis of Gd0.25Ga0.15O0.6/Ga2O3 and HfO2/Al2O3 on In0.53Ga0.47As, adding weight to the suggestion of there being a common defect state distribution and perhaps a common cause of defects states for a number of oxides on In0.53Ga0.47As. [ABSTRACT FROM AUTHOR]

We have performed comprehensive studies of the optical, thermoelectric, and electrical properties of Mg doped InN with varying Mg doping levels and sample thicknesses. Room temperature photoluminescence spectra show a Mg acceptor related emission and the thermopower provides clear evidence for the presence of mobile holes. Although the effects of the hole transport are clearly observed in the temperature dependent electrical properties, the sign of the apparent Hall coefficient remains negative in all samples. We show that the standard model of two electrically well connected layers (n-type surface electron accumulation and p-type bulk) does not properly describe Hall effect in p-type InN. [ABSTRACT FROM AUTHOR]

The admittance characteristics of a well understood oxide system of Gd0.25 Ga0.15 O0.60/Ga2 O3 on In0.53 Ga0.47As are studied at low temperature where the majority of the defect states are frozen. The capacitance-voltage (C-V) characteristics are broadened beyond those expected for an ideal sample. The broadening is ascribed to the presence of a non-uniform surface potential. We report a simple method for measuring the surface potential distribution width using the ac signal amplitude dependence of the C-V profile. A distribution of surface potentials can explain the observed behavior, but only if it includes the admittance of the semiconductor. This is in contrast to the usual approximation that the effect of a distribution of surface potentials on the admittance of the semiconductor is ignored. It is found that the charge state of defect states in the oxide and variation in the doping density of the substrate contribute to the broadening. The implications for inclusion of the semiconductor admittance for the interpretation of ideal characteristics and for the analysisof characteristics with interface states are explored. Both the conductance method and the quasi-equilibrium C-V methods are affected to some extent. An alternative method that can more accurately extract information from the admittance characteristics of the MOS samples is proposed. [ABSTRACT FROM AUTHOR]

The admittances and subthreshold characteristics of capacitors and MOSFETs on buried InxGa1-xAs channel wafers with a dielectric stack of Gd0.25Ga0.15O0.6/Ga2O3 deposited on GaAs and In0.53Ga0.47As are reported. Both the GaAs and InGaAs interface samples show admittance characteristics indicative of the presence of defect states within the oxide, in agreement with previously reported data from the same oxides on n+ substrates. The interface state model is applied to the admittance data to extract an apparent interface state density (Dit) that includes interface and oxide states. The Dit profiles are very different and have pronounced effects on the device performance. The device subthreshold swings (SS) at low source-drain voltages are also used to extract an apparent Dit. A simple method is used to estimate the Fermi-level position within the bandgap (Et) at threshold, and the resulting Dit(Et) are found to be in good agreement with the admittance data. The importance of proper interpretation of SS and Dit in general and in GaAs interface devices in particular is emphasized. A model that accounts for the logarithmic sweep rate dependence of the extracted Dit due to the presence of oxide states is reported and used to estimate their density from SS measurements. The implications of the band parameters of an oxide with defect states within it for the comparison of different oxides on the same substrate and the issues around the comparison of results in general are discussed. [ABSTRACT FROM AUTHOR]

The electrical characteristics of n+ GaAs and In0.53Ga0.47As MOS capacitors with a dielectric stack of Ga2O3/Gd0.25Ga0.15O0.6 have been examined in detail and compared to the interface state model. The deviations from the model are assessed and the limitations of different interface state density extraction techniques are highlighted. The results of a model which accounts for many of the electrical characteristics of the InGaAs material by including states within the oxide and at the interface are reported. A hypothesis that may explain the difference between the GaAs and InGaAs characteristics and the similarities between the properties of many different oxides on InGaAs is discussed, leading to suggestions on how the oxide quality may be improved. [ABSTRACT FROM AUTHOR]

The 300-K admittance characteristics of n+ In0.53Ga0.47As MOS capacitors with a dielectric stack of Gd0.25Ga0.15O0.6/Ga2O3 in as-grown condition are examined in detail and compared to an oxide trap model that we previously introduced. The model explains many of the observed features not contained in the interface state model. By fitting the model to experimental data, we extract a distribution of defect states in space and energy within the oxide and at the oxide/semiconductor interface separately. Oxide states are the dominant defects over a wide range of energy. The defect state densities are not subject to the usual resolution limits of conventional analyses. Using this approach, it is possible to characterize relatively rapidly a wide range of energies at a single temperature without the need for reaching the low or high limits of frequency. The implications for the conventional interface state density (Dit) extraction techniques are explored. It is shown how oxide states can affect the extraction of sample parameters, particularly the insulator capacitance, and can result in a range of extracted Dit values. We believe these contribute to the wide range of Dit reported in the literature from similar admittance characteristics of a number of oxides on In0.53Ga0.47As. [ABSTRACT FROM AUTHOR]