Superlattices and Microstructures, Vol. 2, No. 7, 1986 49 TUNNELLING AND HOT ELECTRONEFFECTS IN SINGLE BARRIER (AlGa)As/GaAs HETEROSTRUCTURE DEVICES L. Eaves, P. S. S. Guimaraes, B. R. Snell, F. W. Sheard, D. C. Taylor, G. A. Toombs Department of Physics, University of Nottingham, NG7 2RD, UK J. C. Portal, L. Bmowaki* LPS, INSA, 31077 Toulouse and SNCI-CNRS, Grenoble, 38042, France K. E. Singer Department of Electrical Engineering and Electronics, UMIST, PO Box 88, Manchester, M60 lQD, UK G. Hill, M. A. Pate Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield, Sl 3JD, UK (Received 11 January 1986) Experimental investigations of the effect of hydrostatic pressure (up to 15 kilobar) and magnetic field (up to 11 T) on the low temperature J(V) characteristics of single barrier n+GaAs/(AlGa)As/n-GaAs/n+GaAs tunnelling structures are reported. The pressure dependence is accurately described by the effective mass/WKB model up to 10 kilobar. At higher pressure the observed breakdown of the model indicates the onset of band structure effects associated with the higher conduction band minima. The reduction of the tunnelling current in an applied magnetic field is discussed in terms of the effect of the diamagnetic energy in increasing the effective height of the barrier. The paper reviews recent models that have been proposed to explain the origin of the oscillatory structure of period AV = fiwL/e observed in the low temperature reverse bias J(V) characteristics. 1. Introduction The need for a thorough understanding of the physics of tunnelling through semiconductor heterostructure barriers is emphasised not only by the large volume of work already done on superlattice structures (see ref. 1) but also by the recent emergence of new devices which rely on quantum tunneliing through only a limited number of barriers’, St *. To date, even the effects associated with tunnelling through a single barrier structure are either not fully understood or remain controversial. Recent work by Hickmott et a15p6,7,8 and by ourselvesg-‘s has demonstrated that simple heterostructure barrier systems of the type n+GaAs/ (AlGa)As/n-CaAs/ n+GaAs display a wide range of quantum and hot electron effects in their current voltage J(V) and capacitance- voltage C(V) characteristics. During the last few months several different models’0~‘2-‘6 have emerged for the origin of the remarkable oscillatory structure with period AV = &L/e which Hickmott et al. and ourselves have observed *On leave from High Pressure Research Center, Polish Academy of Sciences, 01-142. Warsaw, Poland. in the J(V) characteristics of the devices at low temperature and under reverse bias conditions. This article considers three aspects of the behaviour of these single barrier devices. In section 3, we report new investigations on the low temperature J(V) characteristics as a function of hydrostatic pressures up to 15 kilobar. This is an extension of our previous work up to 10 kilobar and reveals evidence of a breakdown of the effective mass/WKB theory of quantum tunnelling through the (AlGa)As barrier. Section 4 describes the effect of magnetic field on the tunnelling current and shows that the decrease of the tunnelling current with magnetic field can be understood qualitatively in terms of the effect that the diamagnetic energy has in increasing the effective height of the tunnelling barrier. Finally, in section 5, we comment on the several recent models proposed for the origin of the oscillatory structure in the reverse bias J(V) characteristics, with special emphasis on that by Ihm16. 2. Structure of the devices The structures used in our study were grown by MBE and consist of the following layers: 200 km thick n+GaAs substrate doped to 2 x 10’. 0749-6036/86/020049+07$02.00/0 @ 1986 Academic Press Inc. (London) Limited