Single-Crystal Y2O3 Epitaxially on GaAs(001) and (111) Using Atomic Layer Deposition

Single-crystal atomic-layer-deposited (ALD) Y₂O₃ films 2 nm thick were epitaxially grown on molecular beam epitaxy (MBE) GaAs(001)-4 × 6 and GaAs(111)A-2 × 2 reconstructed surfaces. The in-plane epitaxy between the ALD-oxide films and GaAs was observed using in-situ reflection high-energy electron diffraction in our uniquely designed MBE/ALD multi-chamber system. More detailed studies on the crystallography of the hetero-structures were carried out using high-resolution synchrotron radiation X-ray diffraction. When deposited on GaAs(001), the Y₂O₃ films are of a cubic phase and have (110) as the film normal, with the orientation relationship being determined: Y₂O₃(110)[001][1¯10]//GaAs(001)[110][11¯0]. On GaAs(111)A, the Y₂O₃ films are also of a cubic phase with (111) as the film normal, having the orientation relationship of Y₂O₃(111)[21¯1¯][011¯]//GaAs(111)[2¯11][01¯1]. The relevant orientation for the present/future integrated circuit platform is (001). The ALD-Y₂O₃/GaAs(001)-4 × 6 has shown excellent electrical properties. These include small frequency dispersion in the capacitance-voltage (CV) curves at accumulation of ~7% and ~14% for the respective p- and n-type samples with the measured frequencies of 1 MHz to 100 Hz. The interfacial trap density (D_it) is low of ~10¹² cm⁻²eV⁻¹ as extracted from measured quasi-static CVs. The frequency dispersion at accumulation and the D_it are the lowest ever achieved among all the ALD-oxides on GaAs(001).