Electrical properties and device applications of InAlP native oxide/GaAs MOS structures

The native oxide of InAlP has been investigated for its electrical properties and usefulness in high-performance electronic devices. InAlP native oxide/GaAs MOS capacitors have been fabricated for use as diagnostic devices, and the electrical properties of InAlP native oxide/GaAs MOS structures have been determined from electrical measurements of these devices. Leakage current measurements suggest that the InAlP oxide has good insulating properties for oxide layers as thin as 11 nm. Capacitance-voltage measurements and impedance spectroscopy indicate that the InAlP oxide/GaAs MOS structure has a relatively low interface state density of 8*10^11cm^-2. This density of interface states is sufficiently low to suggest field-effect transistors using InAlP native oxide as the gate insulator should be possible. Field-effect transistors using InAlP native oxide/GaAs structures have also been explored, resulting in the first demonstration of GaAs MOSFETs using InAlP oxide as the gate dielectric. Two different fabrication procedures for GaAs-based MOSFETs have been developed. One uses the mesa isolation technique, and the other uses oxygen ion implantation and regional oxidation techniques. Both the DC and RF characteristics of fabricated MOSFETs have been evaluated. For mesa-isolated MOSFETs, a 2 um gate length device showed a 63.8 mS/mm peak intrinsic transconductance, and for implant isolated MOSFETs, a 1 um gate length device showed a 105 mS/mm peak intrinsic transconductance and 2.53 GHz cut-off frequency. The measured MOSFET performance has been compared to theoretical expectations based on simplified, idealized device models. The measured DC characteristics of fabricated InAlP oxide/GaAs MOSFETs fall below the theoretical predictions in terms of drain current and transconductance, while the measured RF results show that the devices have lower cut-off frequencies than expected from simple theoretical models. Van der Pauw measurements have been performed on the heterostructures, and measurement results suggest the oxidation conditions, including time and temperature, cause degradation of the GaAs channel material properties. In particular, the channel mobility and carrier concentration are observed to decrease following oxidation of the InAlP layer in the MOSFET heterostructure. This degradation appears to be related to material growth and oxidation conditions, and may be improved by optimizing the heterostructure growth and processing conditions.