V.W.L. Chin

Electron mobilities in gallium, indium, and aluminum nitrides

Electron mobilities in GaN and InN are calculated, by variational principle, as a function of temperature for carrier concentrations of 1016, 1017, and 1018 cm−3 with compensation ratio as a parameter. Both GaN and InN have maximum mobilities between 100 and 200 K, depending on the electron density and compensation ratio, with lower electron density peaking at lower temperature. This is due to the interplay of piezoelectric acoustic phonon scattering at low carrier concentrations and ionized impurity scattering at higher carrier concentrations. Above 200 K, polar mode optical phonon scattering is the mobility limiting process. The 300 and 77 K electron and Hall mobilities as functions of carrier concentration in the range of 1016–1020 cm−3 and compensation ratio are also calculated. The theoretical maximum mobilities in GaN and InN at 300 K are about 1000 and 4400 cm2 V−1 s−1, respectively, while at 77 K the limits are beyond 6000 and 30 000 cm2 V−1 s−1, respectively. We compare the results with experimen...

Evidence for multiple barrier heights in P-type PtSi Schottky-barrier diodes from I-V-T and photoresponse measurements

Abstract Current-voltage-temperature ( I - V - T ) characteristics of p -type moderately doped PtSi Schottky barrier diodes have been measured as a function of temperature from 77 to 120 K. From thermionic emission theory, the saturation current at each temperature is plotted against inverse temperature. According to this theory, the slope should give the barrier height. However, the experimental data obtained do not correlate well with a straight line relationship. These effects are explained by introducing a model in which there is a range of barriers with a normal distribution. A mean barrier of 0.242 eV with a standard deviation of σ = 0.011 eV is obtained. Photoresponse measurements have also been performed at a temperature of 78.0 K to verify the I - V - T results and to test the distributed model. It is found that the cut-off wavelength for PtSi Schottky diodes is well beyond that predicted by a single barrier, giving further evidence for multiple barriers. To test the distributed model, the parameter extracted from the model, i.e. the spread of the barrier, σ is introduced into the photoemission model. The photoyield thereby calculated compares well with experimental results.

Electron mobility in GaSb

Abstract The effect of carrier concentration and compensation on the electron mobilities in GaSb at 300 and 77 K are investigated. Since the energy of the L band minima relative to the Γ band minima in GaSb is reported to range from 0.075 to 0.09 eV, electrons are present in significant amount in both the Γ and L bands at about 150 K and above. Thus, in addition to the impurities and phonons scattering, non-equivalent and equivalent intervalley scattering in both conduction bands are also included in the 300 K calculation. To compare the calculated Hall mobility with the various 300 K experimental data consistently, the electron mobilities in the Γ and L bands are combined using a two band model. This is because experimental electron Hall mobility and electron concentration determined above 150 K are weighted averages of the true values in the two conduction bands. It is found that the correlation for the heavily doped bulk samples are good while for the lighter doped thin epilayers, the calculated mobilities are at least 20% higher. We attribute this to several effects present in the real samples and the growth conditions which are not taken into consideration in the calculations. The 77 K highly doped bulk and best MBE data are also found to correlate reasonably well with the calculated values. We have also numerically fitted all the electron mobilities calculated to a l th polynomial in carrier concentration which may facilitate device modelling.

Alloy‐scattering dependence of electron mobility in the ternary gallium, indium, and aluminum nitrides

Based on Phillips’ electronegativity theory [Rev. Mod. Phys. 42, 317 (1970)] we have determined the alloy scattering potential for the ternary nitrides, Ga1−xAlxN, In1−xGaxN, and In1−xAlxN, and hence the 300 and 77 K electron mobilities through a variational principle calculation. Alloy scattering is important in In1−xGaxN, and In1−xAlxN, both of which show a significant composition ‘‘bowing’’ in electron drift mobility, even at 300 K. This contribution is not important in Ga1−xAlxN. Acoustic phonon scattering is also significant at 300 K, in contrast to the situation obtained in GaAs‐based ternaries.

Correlation between current‐voltage and capacitance‐voltage Schottky barrier height on (100) and (110) GaAs and (110) InP surfaces

Recently, systematic studies of the electrical properties of both n‐ and p‐type Schottky diodes formed by a large number of metals on GaAs of both (100) and (110) orientation and on (100)‐oriented InP have been reported. Current‐voltage (I‐V) and capacitance‐voltage (C‐V) measurements were carried out and the barrier heights were evaluated in these studies. In this paper, these I‐V zero‐bias barrier heights have been correlated with the ideality factors of these diodes. Resulting from this modified barrier height approach is a more fundamental flat‐band (zero‐field) barrier which compares remarkably well with the reported values from the C‐V measurements. In addition, the sum of the modified n‐ and p‐type flat‐band barrier heights for the GaAs (100) and InP (110) Schottky diodes is in better agreement with the band gap for each of the different metals used than the initially reported results.

Electron mobility in InAs1−xSbx and the effect of alloy scattering

The significance of alloy scattering on the electron mobility of InAs1−xSbx is studied in detail. Since little experimental data are available for the InAs1−xSbx compound, calculations of the electron mobility of the binary InAs and InSb semiconductors are first evaluated from the average momentum relaxation times, 〈τm〉 of the individual mechanisms (comprising ionized and neutral impurities, acoustic phonon deformation potential and piezoelectric, optical phonon deformation potential and polar) so that they can be compared to available experimental results. Having ensured that the calculated data are in good agreement with the experimental results in these binary compounds, the electron mobility of the ternary, InAs1−xSbx as a function of x at 77 K and 300 K is calculated by introducing an alloy scattering term. At 77 K, for a total doping concentration of ≂1017 cm−3, the electron mobility of InAs1−xSbx is limited by ionized impurity scattering and alloy scattering is insignificant. However, for doping concentration of ≂1015 cm−3, alloy scattering is found to be the most significant process from about x=0.1 to 0.8. At 300 K the alloy scattering reduces the total electron mobility from between a few percent at x=0.15 to a maximum of about 11% for x=0.60. It is observed that alloy scattering is greatest at x=0.15 but it still is about 11% of the total electron mobility at this composition. The alloy mobilities at 77 K for x=0.6 and x=0.15 are 1.28×106 cm2 V−1s−1 and 7.96×105 cm2 V−1s−1, respectively. The mobilities at x=0.60 are further evaluated as a function of the doping carrier concentration at 77 and 300 K. It is found that alloy scattering becomes increasingly significant for lightly doped semiconductors at low temperatures.The significance of alloy scattering on the electron mobility of InAs1−xSbx is studied in detail. Since little experimental data are available for the InAs1−xSbx compound, calculations of the electron mobility of the binary InAs and InSb semiconductors are first evaluated from the average momentum relaxation times, 〈τm〉 of the individual mechanisms (comprising ionized and neutral impurities, acoustic phonon deformation potential and piezoelectric, optical phonon deformation potential and polar) so that they can be compared to available experimental results. Having ensured that the calculated data are in good agreement with the experimental results in these binary compounds, the electron mobility of the ternary, InAs1−xSbx as a function of x at 77 K and 300 K is calculated by introducing an alloy scattering term. At 77 K, for a total doping concentration of ≂1017 cm−3, the electron mobility of InAs1−xSbx is limited by ionized impurity scattering and alloy scattering is insignificant. However, for doping co...

Dislocation scattering effects on electron mobility in InAsSb

Heteroepitaxial InAsSb is routinely prepared on InAs, InSb, or GaAs substrates under conditions favorable to dislocation formation, since the binary components are lattice mismatched by about 7.4%, and the ternary are mismatched to GaAs by between 7.2% and 14.5%, depending on composition. We here extend the description of electron scattering in InAsSb to include the effects of grain boundaries and dislocations. Comparison with experiment confirms that dislocation scattering has a strong effect on transport, while alloy scattering limits mobility in ternary samples grown with a minimum of defects.

Characteristics of p‐type PtSi Schottky diodes under reverse bias

The characteristics of p‐type PtSi Schottky diodes are determined under reverse bias at cryogenic temperatures. Zero‐bias and flat‐band barrier heights of 0.242 and 0.263 eV, respectively, are evaluated from the data. In addition, the observed lack of excess barrier lowering (other than the image force lowering) is discussed. This excess barrier lowering has previously been postulated to arise from the penetration of the tail end of the metal wave function into the midgap of the semiconductor. Reverse activation analysis is reported for 30 Schottky diodes and an average experimental effective Richardson constant of 45 A/cm2  K2 is determined. The difference from the theoretical value (32 A/cm2 K2) is attributed to the temperature coefficient of the barrier height. A value of 2.7×10−5 eV/K for this coefficient is obtained, which is at least one order of magnitude smaller than the variation of the bandgap of silicon. This provides further evidence that the barrier of the p‐type PtSi Schottky diode is pinned...

Current transport mechanisms studied by I-V-T and IR photoemission measurements on a P-doped PtSi Schottky diode

Abstract The forward bias current of a moderately p-doped PtSi Schottky diode has been studied in detail over a temperature range of about 80–160 K. These investigations are complemented with photoemission measurements using the same device. In the temperature range of 80 to around 110 K, the forward bias current mechanism is found to be thermionic emission over the barrier, with an ideality factor n of around unity and a zero bias barrier height of 0.253 eV, in a good agreement with the photoemission results. Above 110 K, the ideality factor increases rapidly, to about 2.3 at 150 K. The apparent zero bias barrier height is about 0.253 eV between 80–110 K, but falls rapidly at higher temperatures to about 0.24 eV at 150 K. These results suggest that other mechanisms contribute significantly to the current transport of the p-doped PtSi Schottky diode at higher temperatures, and diffusion is found to be responsible. A numerical routine is then used to fit the higher temperature experimental data to a combined thermionic-diffusion theory. The zero-bias barrier height, acceptor density and series resistance obtained from this numerical modelling are in good agreement with the results obtained in the lower temperature region and by internal photoemission measurements. The current mechanisms of a moderately p-doped PtSi Schottky diode over the large temperature range, including that of lower temperature (T ν > μ E , where ν, μ and E are the average velocity of the charge carrier, hole mobility and electric field respectively.

Ohmic contacts to n-type and p-type GaSb

Abstract We report the specific contact resistance at zero bias, Rc, and the barrier heights of rapidly thermally alloyed AuGe contacts on 1017 cm−3 n-GaSb. An alloying step of 1 min at about 300°C provides a minimum contact resistance of about 0.4 Ωcm2. Addition of Ni in the form of a AuNiGe process has little effect on Rc, but reduces the minimum alloying temperature to about 250°C. The further step of an added gold overlayer in the Au AuNiGe process further reduces the minimum alloying temperature to about 200°C. For contacts on 1017 cm−3 p-GaSb, TiAu proved superior in conductance compared to Ti and Cr. Alloying at 300°C slightly improved the quality of the contacts. The optimized processes provide compatible bipolar ohmic metallization for minimum thermal budget.