Submicron Epitaxial Films for GaAs Field Effect Transistors

Abstract

Uniform submicron epitaxial films have been prepared by an optimized version of the ASCl3 , Ga, H2 process. Film requirements and properties of films necessary for high performance normalGaAs FET's are discussed. Growth rate dependences of the Ga source and substrate temperature are shown. Growth rate dependence upon the ASCl3 mole fraction and mass transport effects are shown in the range of interest. Effects of the thermal gradient imposed during deposition are related to the film thickness and doping uniformity obtained with a 5°C/cm and 0.5°/cm process. Vapor doping from H2S and Sn‐doped Ga sources is discussed and related to the character of the epitaxial doping profile. Epitaxial films grown by this technique have been produced in the range of 0.2–04µ with variations in film thickness and doping of < ±10%.

Hydride VPE Growth of GaAs for FET's

“…Less than 3% decomposition was detected in all cases. (ii) A similar increase of doping level in buffer layers grown by the AsC13 VPE technique has been reported (4,18). The effect was attributed to the out-diffusion of an acceptor from the substrate to compensate the adjacent section of the buffer layer.…”

“…In LPE and AsC13 VPE systems, the buffer layer is usually simply an undoped layer. Values of ND --NA of ~5 X 1013 cm -3 have been reported by many workers for both the AsC13 system (3,4,11) and the LPE system (1,2,11). The hydride system is typically characterized by much larger residual doping levels in the range 10zh-10 TM cm -~ although doping levels in the 5 X 1014 cm-~ range have been claimed for specially selected AsH8 and HC1 cylinders (7).…”

“…The Multiple layer structures.--FET's fabricated in VPE material grown directly on Cr-doped substrates were found to have back-biasing problems, i.e., the transconductance of one FET under a given bias was found to be affected by the bias on an adjacent device or by the application of a bias to the substrate. This effect is occasionally observed in LPE material also and is thought to be due to states, possibly acceptors, at the substrate/epilayer interface (4,17,18). To avoid this and to effectively isolate the active region from the substrate, it is desirable to grow a buffer layer between the n epilayer and the substrate.…”

“…GaAs epitaxial layers for microwave devices are usually grown by either LPE from a Ga-rich melt (1,2) or by VPE using the AsCls technique (3)(4)(5). Less extensive work has been performed on the hydride (AsHa + HC1 + Ga) VPE technique (6)(7)(8) and recently molecular beam epitaxy (MBE) has been shown to be suitable for GaAs FET devices (9).…”

“…The reason for the limited utilization of the hydride VPE process which has been highly developed for GaASl-xP= LED applications lies in the fact that the residual impurity level of GaAs grown by this technique is relatively high, typically 1015-10 TM cm -3 (6,8,10). LPE and AsCI~ VPE processes routinely produce material with ND --NA < 1014 cm -3 and ~7~ > 105 cm2/V sec (1)(2)(3)(4)(5)11). For Gunn effect devices, such low doping levels are required.…”