Amitabh Chandra

Surface and interface depletion corrections to free carrier-density determinations by hall measurements

Errors in the determination of (ND-NA) for semiconductor epitaxial layers by the Hall method can result if corrections for carrier depletion are omitted in the calculations. Simple practical procedures are discussed to correct for carrier depletion that occurs in epitaxial layers at their free surfaces, and their interfaces with semi-insulating substrates. Theoretical estimates of carrier depletion in GaAs indicate that depletion regions can extend several microns into high purity epitaxial layers, and can cause (ND-NA) to be considerably underestimated. Experimental evidence is presented in support of the theory.

Quantum mechanical reflection at triangular ‘‘planar‐doped’’ potential barriers for transistors

The quantum mechanical reflection of electrons attempting to overcome the quasitriangular collector potential barrier in a planar‐doped barrier transistor (PDBT) is an undesirable phenomenon that needs to be minimized. We describe a numerical technique for calculating the quantum mechanical reflection and transmission coefficients at triangular potential profiles that approximate the collector barrier of the PDBT. The results of these calculations, and the conclusions drawn, are presented.

A study of alloy scattering in Ga1−xAlxAs

The temperature dependence of electron mobility of high‐purity LPE Ga1−xAlxAs layers (x<0.18) has been studied in the range 25–110 °K to measure the extents of alloylike and ionized impurity scattering. Values of the alloy scattering parameter EB (which may include a contribution from space‐charge scattering) determined for these samples were found to lie in the range 0.36–0.51 eV, the average being 0.44 eV. The compensation ratio was found to be about 2, and independent of x.

The Liquid Phase Epitaxial Growth of High Purity Ga1 − x Al x As

Abstract : We report the high purity in the LPE growth of n Ga(1-x)Al(x)As (O = x or .3) at 700 - 675 C. Carrier concentrations at or below 10 to the 15th power/cc have been consistently obtained, the lowest value achieved being under 3 x 10 to the 14th power/cc at x = .15. It has been shown that these low carrier concentrations do not result from a high compensation ratio. We believe that a dominant shallow donor impurity (thought to be sulphur) is introduced into the melt with the aluminum. We find that the second epigrowth from a melt is significantly purer than the first, presumably due to the extra baking.

Rectification at n‐GaAs–n‐Ga0.7Al0.3As heterojunctions grown by liquid phase epitaxy

Heterojunctions between n‐type GaAs (2×1014cm−3, 1017cm−3) and high purity n‐type Ga0.7Al0.3As (∠1×1015cm−3) have been grown by LPE at 700°C, and significant current rectification has been observed across them at room temperature. At low temperatures, the current drops and the degree of rectification increases considerably. The reverse current characteristic shows reasonable semiquantitative agreement with theoretical I–V curves, calculated by using a thermionic emission model. The N–W profile (where N is the concentration and W the depth) measured across the interface indicates qualitatively the presence of a dipolar space–charge region, as expected.

A study of the conduction properties of a rectifying nGaAs-n(Ga, Al)As heterojunction

Abstract The I – V characteristics of a rectifying n GaAs- n Al x Ga 1- x As heterojunction ( x ≈ 0.28) have been measured over a temperature range of 145–300°K and compared with theory. The non-saturating behavior of the reverse current can be explained by using the graded gap model for the heterojunction. The conduction band-edge step at the interface, determined from these measurements, is 280 meV, in good agreement with existing evidence. This model however fails to account for the forward current, which exhibits an anamolous “pseudo-saturation” behavior. The forward characteristics are qualitatively explained by including in the model deep-level states near the interface, which become negatively charged under forward bias.