The control and modification of metal-semiconductor interfaces using multi quantum barriers

In this paper we report, for the first time, on the effect of placing a multi quantum barrier (MQB) near the gold-Al0.3Ga0.7As interface. A theoretical model has been developed to determine the effective barrier height for a given Schottky-MQB structure directly from the reflectivity calculated as a function of electron energy, RvE. The abruptness and shape of the RvE curve were used to characterise the enhancement efficiency owing to the presence of the MQB. Based on the results of this, a metal-Al0.3Ga0.7As sample containing an MQB structure (Al0.3Ga0.7AsGaAs) was designed and grown by molecular beam epitaxy. A standard metal-Al0.3Ga0.7As Schottky barrier (with no MQB), was also grown for comparison. Gold Schottky contacts were formed and the barrier height measured, using a current-voltage technique, in-situ to avoid degradation on exposure to air. In addition, capacitance-voltage, and ballistic electron emission microscopy were used to further characterise the interfaces ex-situ. The experimentally measured barriers of both samples were found to be in excellent agreement with the theoretical predictions from the reflectivity curves. The dependence of the barrier height enhancement on the structure and composition of the MQB is also discussed.