Sorab K. Ghandhi

General theory for pinched operation of the junction-gate FET

Abstract A device oriented model is developed to describe the operation of the junction-gate field-effect transistor (FET) beyond pinch-off. The model is derived on the basis of a generalized structure with an arbitrary channel doping profile. It provides a qualitative and quantitative description of the current conduction mechanism, and is applicable over the entire dynamic range of device operation. Current conduction mechanisms in the vicinity of the source and the drain are examined separately. It is shown that the saturation of carrier drift velocities at high electric fields results in formation of a drain space-charge region of finite length. An approximate solution of the two-dimensional Poissons equation is developed to describe the potential distribution within this region. A significant result of the device model is the prediction of a finite drain resistance in pinched operation, which shows a strong dependence on the device operation point.

Crystallographic tilting of heteroepitaxial layers

Abstract Mismatched heteroepitaxial layers generally exhibit a crystallographic tilt with respect to their vicinal substrates, but this phenomenon is poorly understood. Two models have been proposed for tilted epitaxy previously. The Nagai model considers the mismatch at surface steps on vicinal substrates and the misfit dislocation theory considers misfit dislocations with inclined Burgers vectors as the primary cause of tilted epitaxy. Neither of these theories applies in the general case, however. The misfit dislocation theory does not consider the mechanism of the preferential introduction of dislocations with a particular orientation, and therefore does not predict the direction of tilted epitaxy. Here a general theory for tilted epitaxy is proposed, including both contributions cited above. We propose that the preferential glide of certain Burgers orientations is the result of vicinal substrates, commonly used in heteroepitaxy, which create an assymetry in the stresses for the various active slip systems. If the substrate inclination is about an axis of symmetry, then the tilt of the epitaxial growth is about the same axis, and its sign is determined by the nature of the mismatch: the relief of compressive strain results in negative tilt whereas the relief of tensile strain results in positive tilt. The exact amount of tilt will depend on the dynamics of strain relaxation. Upper and lower limits for the tilt have been derived. The observed tilt angle contains information on how the relaxation process took place.

Highly oriented zinc oxide films grown by the oxidation of diethylzinc

Zinc oxide films, with a high degree of c‐axis orientation, have been grown on glass substrates by a chemical vapor deposition process involving the oxidation of diethylzinc. Film growth was carried out over the 200–500 °C temperature range; however, the maximum crystal orientation was found to occur with substrate temperatures between 325 and 400 °C. The effect of different substrate materials on crystallographic orientation is also described in this letter.

Analytical solutions for the breakdown voltage of abrupt cylindrical and spherical junctions

Abstract Analytical solutions for the breakdown voltage of abrupt cylindrical and spherical junctions have been obtained, using suitable approximations for the electric field in the depletion layer. These solutions are shown to be within ±1% of exact computer solutions for doping densities of less thant 10 16 cm −1 . By normalization to the parallel plane case, these solutions have been presented in a form which allows the computation of the breakdown voltage of both cylindrical and spherical junctions using a single curve for each situation.

Ultraviolet‐Enhanced Oxidation of Silicon

This paper describes the results of dry thermal oxidation of silicon under uv‐irradiation conditions. A model is proposed to explain the enhanced oxidation and reduced surface‐state charge density that occur under these conditions.

Morphology of organometallic CVD grown GaAs epitaxial layers

Abstract Growth conditions and resulting epitaxial layer morphology are presented for atmospheric pressure OM-CVD layers of GaAs, grown at 700°C on (100), (100) + 3° → 〈110〉, (110), (111)Ga, and (111)As oriented substrates. The substrate orientation found most favorable for useable devices is either the (100) or misoriented (100). For these substrates, the epitaxial layer morphology is largely independent of reactant flux, in contrast to the results found for the other orientations. A simple model is presented to explain the morphology of layers grown on the (111)As and (111)Ga faces. Finally, impact of the morphology study on the electrical characteristics of the layers, and on the growth of polycrystalline layers, is discussed in this paper.

Ion-cleaning damage in (100) GaAs, and its effect on schottky diodes

Abstract This study investigates the effect of ion cleaning damage of (100) GaAs in the 100–1000 eV range, and also its recovery with thermal annealing to 400°C. It is shown that GaAs could be annealed to a considerable extent if the ion-damage was ⩽ 100 eV. However, full recovery was not achieved. On the other hand, samples damaged at ⩾ 400 eV became progressively worse with annealing. Measurements indicate that these samples are dominated by the effect of arsenic variances within the bulk. These remain in the bulk, but are distributed spatially upon annealing. They behave as deep donors, so that the net electron concentration in the bulk is enhanced. Aluminum-n GaAs Schottky diodes were used as a vehicle for this study.

Growth of silica and phosphosilicate films

Investigations of the reaction kinetics of the deposition of silica and phosphosilicate glasses were made to determine the parameters governing the rates of reactions. Dependence of deposition rates on substrate temperature shows that the reactions obey the absolute rate theory of heterogeneous reactions at a solid surface. The silane oxidation reaction is of half‐order with respect to oxygen, of half‐order with respect to silane, and of first‐order over‐all. The phosphine oxidation reaction is of second‐order over‐all. The unusual decrease in deposition rate with increasing oxygen concentrations, during the oxidation of silane, has been shown to originate from the adsorption of oxygen on the silicon substrates, retarding the reaction.

Electrical Properties of Organometallic Chemical Vapor Deposited GaAs Epitaxial Layers Temperature Dependence

Depots realises sur des supports (100) entre 450 et 1050°C, pour diverses conditions de croissance. Les couches obtenues a 1050°C sont du type p et la concentration en trous diminue quand la temperature de croissance diminue. En dessous de 975°C, on obtient des couches de type n. La concentration en electrons est maximale a 850°C

High quality Hg1−xCdxTe epitaxial layers by the organometallic process

An organometallic process for the epitaxial growth of Hg1−xCdxTe is described in this letter. This process involves the simultaneous pyrolysis of dimethylcadmium and diethyltelluride in mercury vapor at 415 °C, using hydrogen as the carrier gas. It is shown this process results in device quality layers of uniform composition. Layers with x=0.17 exhibited n‐type conduction, with an approximate carrier concentration of 3.8×1015 cm−3, and a Hall mobility of 2.45×105 cm2/Vs at 77 K. Thus, they are comparable to the best grown by liquid phase epitaxy. A p‐type layer, with anomalous electrical characteristics, has also been described in this letter. Reasons for these anomalous characteristics are outlined briefly.