Semiconductor Resonant Tunneling Device Physics and Applications
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SEMICONDUCTOR RESONANT TUNNELING DEVICE PHYSICS AND APPLICATIONS MARK A. REED, ALAN C. SEABAUGH, YUNG-CHUNG KAO, JOHN N. RANDALL, WILLIAM R. FRENSLEY, AND JAMES H. LUSCOMBE Central Research Laboratories, Texas Instruments Incorporated, P. 0. Box 655936, M/S 154, Dallas, TX 75265 U.S.A ABSTRACT A discussion of resonant tunneling physics in both diode and transistor heterojunction structures is presented. It is evident the In(GaAI)As/InP system is significantly superior for this application. We also present results on resonant tunneling in lower dimensional systems. INTRODUCTION The initial demonstration [1] and renaissance [2] of resonant tunneling has focused interest in the use of artificially structured heterojunction structures for high speed and/or complex function devices. Additionally, these semiconductor composites have become important physical systems for elucidating relevant carrier transport mechanisms operative on the nanometer scale. Until recently, the bulk of resonant tunneling investigations were performed in the GaAs/(A1,Ga)As system. An often (mis)used figure of merit for a generic double barrier, single quantum well structure is the peak-to-valley current ratio. In the GaAs/(AI,Ga)As system, nearly 4:1 [3] at 300K has been reported. The GaAs-based material system, however, has several important materials limitations which significantly reduce the effectiveness of hot electron transport in comparison to some other systems, specifically the In(GaAI)As/InP system. A comparison of key material properties is shown in Table 1. First, the lower effective mass of the electron in In 0 .53Ga0. 47As means that quantum size effects occur at larger physical dimensions in InO. 53Gao. 47 As compared to GaAs. An example of this can be observed in the characteristics of a wide-well resonant tunneling diode (RTD). Figure 1 shows the room temperature and 4.2K conductance-voltage characteristics of a 40nm InGaAs quantum well (QW) RTD. The structure is symmetric, around the undoped well, with 2 nm AlAs barriers, 60 nm InGaAs lx101 s cm-3 cladders and 5x10 1 3 cm- 3 contacts, on semi-insulating InP. Qualitatively identical 300K conductance oscillations have only been reported previously [4] in a 60 nm Ino.52A10. 4sAs/ Ino.s.3Gao. 4rAs QW RTD. In the GaAs system, negative conductance is observable only at low temperature [5]. Secondly, broader transmission resonance are also expected with lower carrier effective masses which leads to higher peak current densities. In a 1.5 nm AlAs barrier, 5 nm InGaAs (on InP) QW structure, we have observed a peak current density of 2.5x101 A/cm 2 with a /V of 4:1 at 300K. This is comparable to the best reported [6].
Table I. Summary of relevant materials parameters
Structure
GaAs/AlAs/InGaAs on GaAs
InAlAs/AlAs/InGaAs on InP
Effective mass A(r - L) AE, range 300K RTD PVR
0.067 0.3 eV 0.3 4:1
0.041 0.55 eV 0.49 14:1,30:1
Mat. Res. Soc. Symp. Proc. Vol. 198. @1990 Materials Research Society
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