Passivation of InGaAs/InP heterostructures
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are highly reactive to oxygen species; reaction with oxygen gives large surface recombination velocities and high densities of surface states. This is detrimental to device performance and reliability. Therefore, surface passivation of III-V compound semiconductors remains a critical issue for the fabrication of advanced micro-electronic and opto-electronic devices and integrated circuits. Because of their high sensitivity to surface recombination, minority carrier devices such as lasers and heterojunction bipolar transistors (HBTs) can be used as test vehicles for passivation studies [2,6]. In compound semiconductor HBTs the base-emitter surface is crucially important for good device performance. Surface states and associated recombination centres can degrade the performance of HBTs, especially when the emitter-base junction area is small (emitter-size effect [7]). InGaAs-based devices are cited to be better than their GaAs counterparts, because InGaAs has a lower surface recombination velocity than GaAs. Even so, problems of surface recombination have been also reported in InGaAs/InP heterostructures [8-11]. Surface currents have been correlated with leakage paths between the InP emitter side-wall and the base contact [11]. Using a low temperature deposition technique (ECR-PECVD), Fukano et al. [10] found that although the surface currents could be suppressed with a treatment of HF before dielectric deposition, annealing at 200'C regenerated the surface currents, indicating poor thermal stability of the oxide. Recently, Kikawa et al. [12] reported that the Fermi level of an InP 227 Mat. Res. Soc. Symp. Proc. Vol. 573 ©1999 Materials Research Society
surface after Si0 2 deposition shifts closer to the conduction band edge, resulting in a surface leakage path. Thus it appears that the degradation mechanisms in dielectric-coated electronic devices are not yet fully understood. In this study, we discuss the passivation of InGaAs (100) surfaces and its application to InGaAs/InP heterostructures. We illustrate the effects of different treatments on the semiconductor surfaces through high energy-resolution x-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) measurements. First, we discuss the passivation effects of (NH4 )2S on InGaAs (100) surfaces. This treatment has been demonstrated to reduce the surface recombination velocity and enhance the photoluminescence intensity of II-V surfaces [13,14]. Sulfur treatment is now being implemented in the fabrication of various devices [15]. Then we discuss the effectiveness of using a simple dry UV-ozone process to passivate the InGaAs surfaces. This process has been reported to produce uniform thin stoichiometric native oxides [16], and results in good electrical characteristics in NIS diodes [17].
We have integrated the passivation treatments in the fabrication process of InGaAs/InP HBTs, and observed a dramatic increase in the current gain of large-area devices. Unfortunately, the improvement in device characteristics degrades after PECVD dielectric depositi
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