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Al/AlN/InP Metal-Insulator-Semiconductor-Diode Characteristics with Amorphous AlN Films Deposited by Electron-Cyclotron-Resonance Sputtering

Amorphous AlN films deposited by sputtering using electron cyclotron resonance (ECR) plasma were used to form AlN/n-InP metal–insulator–semiconductor diodes. The AlN films were deposited without substrate heating. Capacitance–voltage (C–V) measurements showed a small hysteresis window of ∼35 mV for a 2-nm-thick AlN film, and frequency dispersion was much improved by post-deposition annealing at 200°C in an H2 gas atmosphere. We estimated the interface-trap density to be 3×1012 cm-2eV-1 by comparing 10-kHz and 1-MHz C–V curves. Small leakage currents of less than 2 mA/cm2 at a bias voltage of 1 V were obtained for the 2-nm-thick film. To clarify the effect of the deposition methods, AlN films were deposited by conventional magnetron sputtering. ECR sputtering provided better C–V and current-voltage characteristics than magnetron sputtering for as-deposited AlN films, showing that good metal–insulator–semiconductor (MIS) properties arise because of the suitable deposition method and the good combination of materials. An analysis of surface atoms on the InP substrate by secondary ion mass spectrometry showed a large oxygen concentration on the order of 1022 cm-3, which is not preferable for MIS diode properties. Surface cleaning using dilute HF reduced oxygen and carbon concentrations to less than half.