Capacitive hysteresis effects in 5.0 nm single and double barrier AlAs/GaAs tunneling structures grown by molecular-beam epitaxy

Abstract

Single and double 50 Å AlAs barrier structures with n+ electrode regions and 50 Å GaAs ‘‘spacer’’ layers are examined using impedance-phase measurements, deep level transient spectroscopy (DLTS), and pulsed I–V measurements. Resonant tunneling curves with a peak-to-valley ratio of 2:1 at 300 K are obtained from the double barrier devices. Under thermal stress of temperatures >390 K or large terminal voltage conditions, an abrupt transition from a low impedance, resistive state to a high impedance, capacitively reactive state is observed. The high impedance, reactive state is dynamically observed in all the device structures examined. In many cases, the high impedance state is persistent for extensive periods of time. Repeatable switching between the high and low persistent impedance states can be accomplished by the application of large (1–4 V) terminal voltages. However, both persistent states are stable under small applied biases for long durations. Impedance-phase measurements have been performed on both the low impedance and the persistent high impedance state as a function of frequency for bias levels from −2.0 to 2.0 V. The low impedance state shows a much greater frequency dependence of the resistive and reactive components than the persistent high impedance state. Pulsed I–V measurements of Schottky barrier contacted devices reveal two characteristic I–V curves which are followed qualitatively for all the devices examined. The first is a series resistance limited diode with a turn-on voltage above 1.5 V. The second characteristic, followed after the abrupt switching, is that of a diode-like exponential current dependence on the applied voltage. Single and double barrier devices with Ohmic contacts displayed similar switching behavior at large biases. The persistent nature of the low and high impedance states observed are consistent with the formation and destruction of an inversion layer at the AlAs/GaAs interface. Silicon autodoping of the AlAs barrier regions may also give rise to DX-like hot electron trapping, similar to that observed in low mole fraction Al1−xGaxAs [T. N. Theis, B. D. Parker, P. M. Solomon, and S. L. Wright, Appl. Phys. Lett. 49, 1542 (1986)]. The possibility of a filamentary conduction process is also discussed.