Characterization of ALD Beryllium Oxide as a Potential High-k Gate Dielectric for Low-Leakage AlGaN/GaN MOSHEMTs

The chemical and electrical characteristics of atomic layer deposited (ALD) beryllium oxide (BeO) on GaN were studied via x-ray photoelectron spectroscopy, current–voltage, and capacitance–voltage measurements and compared with those of ALD Al2O3 and HfO2 on GaN. Radiofrequency (RF) and power electronics based on AlGaN/GaN high-electron-mobility transistors are maturing rapidly, but leakage current reduction and interface defect (D it) minimization remain heavily researched. BeO has received recent attention as a high-k gate dielectric due to its large band gap (10.6 eV) and thermal stability on InGaAs and Si, but little is known about its performance on GaN. Unintentionally doped GaN was cleaned in dilute aqueous HCl immediately prior to BeO deposition (using diethylberyllium and H2O precursors). Formation of an interfacial layer was observed in as-deposited samples, similar to the layer formed during ALD HfO2 deposition on GaN. Postdeposition anneal (PDA) at 700°C and 900°C had little effect on the observed BeO binding state, confirming the strength of the bond, but led to increased Ga oxide formation, indicating the presence of unincorporated oxygen in the dielectric. Despite the interfacial layer, gate leakage current of 1.1 × 10−7 A/cm2 was realized, confirming the potential of ALD BeO for use in low-leakage AlGaN/GaN metal–oxide–semiconductor high-electron-mobility transistors.