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AlGaAs-GaAs GATE FIELD-EFFECT TRANSISTOR

IP.com Disclosure Number: IPCOM000038326D
Original Publication Date: 1987-Jan-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Kircher, CJ: AUTHOR [+3]

Abstract

A grown AlGaAs cap is employed over GaAs in an AlGaAs-GaAs gate field- effect transistor (FET). The structure is shown in the drawing. In the drawing, a molecular beam epitaxy (MBE) in situ grown AlGaAs layer is used as a cap. This cap has the immediate advantage of much better control over its thickness and composition properties, intimate contact with the GaAs, very low stress, and ability to withstand a high temperature processing cycle. The cap is of low, about 20%, aluminum mole fraction doped AlGaAs to facilitate ohmic contact, but high enough mole fraction to obtain a good reactive ion etch (RIE) selectivity.

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AlGaAs-GaAs GATE FIELD-EFFECT TRANSISTOR

A grown AlGaAs cap is employed over GaAs in an AlGaAs-GaAs gate field- effect transistor (FET). The structure is shown in the drawing. In the drawing, a molecular beam epitaxy (MBE) in situ grown AlGaAs layer is used as a cap. This cap has the immediate advantage of much better control over its thickness and composition properties, intimate contact with the GaAs, very low stress, and ability to withstand a high temperature processing cycle. The cap is of low, about 20%, aluminum mole fraction doped AlGaAs to facilitate ohmic contact, but high enough mole fraction to obtain a good reactive ion etch (RIE) selectivity. The thickness of the cap is tailored to attenuate a lower energy, high dose ion implant sufficiently, under the overhung region, so that the leakage properties of the gate are not unduly compromised, and yet to allow sufficient dose to achieve a reasonably small sheet resistance in the GaAs under the overhung region. For this, about 100 nm would be satisfactory. A thin GaAs cap is placed on top of the AlGaAs to protect the top surface from oxidation. The following fabrication procedure may be employed for the structure of the drawing. 1. Grow epitaxial layers, including the AlGaAs cap, as shown in the drawing. 2. Gate photoresist stencil. 3. RIE of AlGaAs cap, using endpoint detection and suitable etching parameters for a non-selective etch. A chemical etch could also be used. 4. Change RIE etching parameters t...