Schottky Region Research Articles

Leakage Current Measurements of STO and BST Thin Films Interpreted by the "Dead" Layer Model

Electrical properties of Strontium-Titanate (STO) and Barium-Strontium-Titanate (BST) thin films capacitors were investigated. The STO films were fabricated by chemical solution deposition (CSD) with thickness between 50 and 150 nm, while the BST films were deposited by metal organic chemical vapor deposition (MOCVD) with thickness between 20 and 110 nm. All films were grown on platinized and oxidized silicon wafers. As top electrodes platinum (Pt) was deposited on top of the ceramic film by sputtering. The electrode size varied between 8*10 m 3 to 1 mm 2 . The leakage current measurements were performed at different temperatures ranging from 15 to 200C and the applied voltage varied between 0 and - 4 V. Capacitance was measured at RT up to - 3 V bias at 1 kHz and 50 mV oscillation voltage. The main results are: The effective barrier heights extracted from the temperature dependence of leakage current are about 1.35 eV for STO and 0.94 eV for BST for the temperature region >100C. The field dependencies of the leakage current show almost perfect linear behavior in a "Schottky" plot for BST while STO reveals 2 separated Schottky regions. The permittivity extracted from the field dependence using the simple thermionic emission model with Schottky lowering results in rather improbable values of the effective Richardson constant A * and unphysical values of the relative optical permittivity, l r, opt <1. The use of a modified model with low permittivity interface layers ("dead layers"), as suggested by the thickness dependence of the inverse capacitance, solved these difficulties. The parameters extracted from fits of this model are discussed.

Low forward drop JBS rectifiers fabricated using submicron technology

This paper demonstrates the impact of using submicron technology (0.5 /spl mu/m design rules) on JBS Rectifiers to achieve very low forward voltage drops while maintaining good high temperature reverse blocking characteristics. Two dimensional numerical simulations show that decreasing P/sup +/-junction width and depth improves the on-state voltage drop by improved utilization of the active area for the Schottky region and improved spreading of majority carrier current from the Schottky contact. Experimental results that demonstrate the capability to reduce the forward drop from 0.5 V to 0.25 V, while operating at up to 125/spl deg/C-175/spl deg/C with good reverse blocking capability, are presented. The tradeoff curves between forward drop and reverse leakage current show 45/spl times/ reduction in leakage current for the same forward drop as compared to previous reports on JBS rectifiers. Power dissipation analysis indicates higher operating temperatures, (100/spl deg/C for Ti-JBS and 175/spl deg/C for Cr-JBS rectifiers) with reduced heat sink sizes for the JBS Rectifiers when compared to the conventional Schottky Barrier Diode (SBD).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Controlling the characteristics of the MPS rectifier by variation of area of Schottky region

A method of controlling the characteristics of the merged p-i-n Schottky (MPS) rectifier is demonstrated both theoretically and experimentally. It is based on varying the relative area of the p/sup +/-n junction and Schottky regions in the device. A curve for the tradeoff between the forward voltage drop and the switching characteristics can be obtained using this method, while maintaining a constant minority-carrier lifetime. It is shown that this curve is superior to that obtained for the p-i-n rectifier using lifetime control techniques. This method of performing the tradeoff has the advantage that it can be done at the design stage, avoiding the problems and additional processing associated with lifetime control. It is also demonstrated that the superior characteristics of the MPS rectifier is retained even when a thick high-resistivity epilayer is used for high blocking voltages up to 900 V.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Very low forward drop JBS rectifiers fabricated using submicron technology

The impact of using submicron technology (0.5- mu m design rules) on JBS (junction barrier controlled Schottky) rectifiers is examined. Two-dimensional numerical simulations demonstrate that decreasing P/sup +/-junction width and depth improves the on-state voltage drop. This is due to the improved utilization of the active area for the Schottky region and improved spreading of majority carrier current from the Schottky contact. However, a junction depth of less than 0.3 mu m results in an undesirable high electric field at the Schottky interface during reverse bias, leading to barrier height lowering, which produces a large leakage current. A large reduction in the spreading resistance is possible by increasing the N-epitaxial layer doping and by reducing the cell pitch in order to achieve the same pinch-off voltage. However, increasing the doping above 2*10/sup 16/ cm/sup -3/ reduces the breakdown voltage below 25 V (which is required for 5 V power supplies). The simulations showed that, by using a proper choice of N-doping and P/sup +/-linewidth, one can reduce the leakage by one to two orders of magnitude as compared to a conventional Schottky buried diode. Experiments conducted to verify the simulations clearly demonstrate that the use of submicron technology can lead to significant improvement in JBS rectifier characteristics.

Surface potential studies on Langmuir-Blodgett multilayers and adsorbed monolayers

The surface potential of multilayers of stearic acid, chlorophyll-a, cobalt-substituted chlorophyll and monolayers of a perfluorinated carboxylic acid deposited onto n-type GaP was measured by the Kelvin technique. A comparison is made between the surface potential of clean GaP and the surface potential of GaP onto which various numbers of layers of amphiphilic material have been deposited. The results can be interpreted in terms of a model in which all three materials deposited as multilayers contain p-type defects and a Schottky region thus exists both in the n-type GaP and also in the p-type multilayer.

The brightness of electron beams

An expression is derived for the brightness or directional beam intensity of an electron beam, for a general velocity distribution at the emitting cathode. The result is then specialized to the case of the brightness on the axis in the direction of the axis for a cylindrically symmetric system. In this case the Langmuir law B/J=eV/πkT is shown to hold for emission in the Schottky region even though the velocity distribution is not Maxwellian; and an analogous expression B/J=eV/πd, where d is a function only of the applied field, is shown to hold for field-emitted beams. It is shown that detailed ray tracing is necessary to evaluate the brightness for points not on the axis and directions not in the axial direction.

Space Charge Effect in the Oxide Cathode Layer

It was concluded theoretically that space charge may be formed in the oxide cathode layer near the surface, when electric field at the cathode surface is sufficiently strong so that the diode may be regarded to operate in the Schottky region. The calculations are carried out for one-dimensional model and neglecting the interface layer, which exists usually between the base metal and the oxide coating. As the result of this space charge, the slope of the Schottky plots are several times greater, than that predicted by the Schottky theory for metal surfaces. This space charge may be responsible for the microsecond emission decay observed by Sproull and others.