The Characterization and Passivation of Fixed Oxide Charges and Interface States in the $\hbox {Al}_{2}\hbox {O}_{3}/ \hbox {InGaAs}$ MOS System

In this paper, we present a review of experimental results examining charged defect components in the Al₂O₃/In_0.53Ga_0.47As metal-oxide-semiconductor (MOS) system. For the analysis of fixed oxide charge and interface state density, an approach is described where the flatband voltage for n- and p-type Al₂O₃/In_0.53Ga_0.47As MOS structures is used to separate and quantify the contributions of fixed oxide charge and interface state density. Based on an Al₂O₃ thickness series (10-20 nm) for the n- and p-type In_0.53Ga_0.47As layers, the analysis reveals a positive fixed charge density ( ~ 9 ×10¹⁸ cm^-3) distributed throughout the Al₂O₃ and a negative sheet charge density (- 8 × 10¹² cm^-2) located near the Al₂O₃/In_0.53Ga_0.47As interface. The interface state density integrated across the energy gap is ~1 ×10¹³ cm^-2 and is a donor-type (+/0) defect. The density of the fixed oxide charge components is significantly reduced by forming gas (5 % H₂/ 95% N₂ ambient at 350 °C for 30 minutes) annealing. The interface state distribution obtained from multi-frequency capacitance-voltage and conductance-voltage measurements on either MOS structures or MOSFETs indicates a peak density located around the In_0.53Ga_0.47As midgap energy, with a sharp increase in the interface state density toward the valance band and evidence of interface states aligned with the In_0.53Ga_0.47As conduction band. The integrated interface state density obtained from multi-frequency capacitance-voltage and conductance-voltage analysis is in good agreement with the approach of comparing the flatband voltages in n- and p -type Al₂O₃/In_{- .53}Ga_0.47As MOS structures. Finally, this paper reviews recent work based on an optimization of the In_0.53Ga_0.47As surface preparation using (NH₄)₂S, combined with minimizing the transfer time to the atomic layer deposition reactor for Al₂O₃, which indicates interface state reduction and genuine surface inversion for both n- and p -type Al₂O₃/In_0.53Ga_0.47As MOS structures.