Interface Trap Density Reduction for Al2O3/GaN (0001) Interfaces by Oxidizing Surface Preparation prior to Atomic Layer Deposition.

We correlate interfacial defect state densities with the chemical composition of the Al2O3/GaN interface in metal-oxide-semiconductor (MOS) structures using synchrotron photoelectron emission spectroscopy (PES), cathodoluminescence and high-temperature capacitance-voltage measurements. The influence of the wet chemical pretreatments involving (1) HCl+HF etching or (2) NH4OH(aq) exposure prior to atomic layer deposition (ALD) of Al2O3 were investigated on n-type GaN (0001) substrates. Prior to ALD, PES analysis of the NH4OH(aq) treated surface shows a greater Ga2O3 component compared to either HCl+HF treated or as-received surfaces. The lowest surface concentration of oxygen species is detected on the acid etched surface, whereas the NH4OH treated sample reveals the lowest carbon surface concentration. Both surface pretreatments improve electrical characteristics of MOS capacitors compared to untreated samples by reducing the Al2O3/GaN interface state density. The lowest interfacial trap density at energies in the upper band gap is detected for samples pretreated with NH4OH. These results are consistent with cathodoluminescence data indicating that the NH4OH treated samples show the strongest band edge emission compared to as-received and acid etched samples. PES results indicate that the combination of reduced carbon contamination while maintaining a Ga2O3 interfacial layer by NH4OH(aq) exposure prior to ALD results in fewer interface traps after Al2O3 deposition on the GaN substrate.

Silicon interfacial passivation layer chemistry for high-k/InP interfaces.

The interfacial chemistry of thin (1 nm) silicon (Si) interfacial passivation layers (IPLs) deposited on acid-etched and native oxide InP(100) samples prior to atomic layer deposition (ALD) is investigated. The phosphorus oxides are scavenged completely from the acid-etched samples but not completely from the native oxide samples. Aluminum silicate and hafnium silicate are possibly generated upon ALD and following annealing. The thermal stability of a high-k/Si/InP (acid-etched) stack are also studied by in situ annealing to 400 and 500 °C under ultrahigh vacuum, and the aluminum oxide/Si/InP stack is the most thermally stable. An indium out-diffusion to the sample surface is observed through the Si IPL and the high-k dielectric, which may form volatile species and evaporate from the sample surface.