Orientation-dependent <i>β</i>-Ga2O3 heterojunction diode with atomic layer deposition (ALD) NiO

This work reports the demonstration of ALD-deposited NiO/β-Ga2O3 heterojunction diodes (HJDs) on low doped (ND-NA ≤ 1 × 1016 cm−3) drift layers and highly doped (001) &amp; (100) n+ substrates (ND-NA &amp;gt; 1 × 1018 cm−3) with experimental observation of a parallel-plane junction electric field as high as 7.5 MV/cm, revealing a crystal orientation dependence in β-Ga2O3. We use a metalorganic precursor, bis(1,4-di-tert-butyl-1,3-diazadienyl) (nickel Ni(tBu2DAD)2), with ozone (O3) to deposit NiO. The NiO/β-Ga2O3 HJD on the 7.7 μm-thick HVPE-grown drift region exhibited an on-state current density of ∼20 A/cm2 at 5 V, ∼10−8 A/cm2 reverse leakage at low reverse bias (−5 V), and a rectifying ratio (Jon/Joff) of ∼109. The HJD broke down at ∼2.2 kV reverse bias, corresponding to a ∼3.4 MV/cm parallel-plane junction electric field, with a noise-floor reverse leakage (10−8–10−6 A/cm2, nA) at 80% of the device's catastrophic breakdown voltage. The NiO/β-Ga2O3 HJDs on n+ (001) &amp; (100) highly doped substrates exhibited breakdown voltages at 12.5–16.0 and 28.5–70.5 V, respectively, with extracted critical electric fields (EC) at 2.30–2.76 and 4.33–7.50 MV/cm, revealing a substrate crystal orientation dependence on breakdown electric field for β-Ga2O3. The 7.5 MV/cm EC reported here is one of the highest parallel-plane junction electric fields reported in literature.