Substrate and interface effects in GaAs fet’s

2014 In this paper, the experimental results describing the substrate bias effect on the Schottky gate capacitance-voltage and the DC current-voltage characteristics of GaAs FET’s (N-type epilayer on semi-insulating Cr-doped substrate) are reported. These results are accounted for by the formation of a double space-charge in the N-layer and in the S.I. substrate in the vicinity of the interface. A theoretical analysis is proposed and appropriate methods for obtaining both the N active layer and the interface parameters (fixed interface charge value, deep centers density in the S.I. GaAs) are shown. The deep level charge effect on the low temperature drain current-drain voltage characteristics, is described. REVUE DE PHYSIQUE APPLIQUÉE TOME 13, DÉCEMBRE 1978, Introduction. In gallium arsenide Schottky barrier field-effect transistors, made from N-type epilayer on semi-insulating substrate, it is found that the interface characteristics strongly influence the electrical properties : low-frequency drain current relaxation phenomenon, R.F. and noise performances [1]. In this paper, the experimental results describing the substrate bias effect on the Schottky gate capacitance-voltage and the DC current-voltage characteristics will be reported. It will be shown that a space-charge appears in the N-layer in the interface vicinity. Its properties depend on the interface parameters, i.e. fixed interface charge, deep centers charge in the S.I. A theoretical analysis of the drain current variations will be proposed and applied to the N active layer (thickness, effective doping concentration, carrier mobility) and interface (fixed interface charge value, deep centers concentration in the S.I.) parameters determination. 1. Expérimental results. The studied structures are made from an N-type Ge-doped GaAs layer of thickness d between 0.2 and 0.5 pm. This epilayer (1) Preliminary results conceming this communication have been previously accepted for publication (in French) in the Revue de Physique Appliquée. (2) G.R.E.C.O., Microondes, C.N.R.S. n° 11. is obtained by a low pressure organo-metallic compounds cracking [2] directly on Cr-doped semiinsulating substrate of thickness D equal to 400 gm. The Schottky gate (L = 1 JlII1 or 50 gm, Z = 300 pm is made from an Au-Pt-Ti metallization. The lateral Au-Ge alloyed ohmic contacts are the source and the drain electrodes and, the ohmic contact (Au-Ge) on the S.I. bottom is called the substrate electrode (Fig. 1). FIG. 1. Configuration of the device. Definition of the bias voltages. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:019780013012065500