*Review* **Vertical GaN-on-GaN Schottky Diodes as** α**-Particle Radiation Sensors**

**Abhinay Sandupatla 1,\*, Subramaniam Arulkumaran 2,3, Ng Geok Ing 1,2,\*, Shugo Nitta 3, John Kennedy 4 and Hiroshi Amano 3**


Received: 16 April 2020; Accepted: 8 May 2020; Published: 20 May 2020

**Abstract:** Among the different semiconductors, GaN provides advantages over Si, SiC and GaAs in radiation hardness, resulting in researchers exploring the development of GaN-based radiation sensors to be used in particle physics, astronomic and nuclear science applications. Several reports have demonstrated the usefulness of GaN as an α-particle detector. Work in developing GaN-based radiation sensors are still evolving and GaN sensors have successfully detected α-particles, neutrons, ultraviolet rays, x-rays, electrons and γ-rays. This review elaborates on the design of a good radiation detector along with the state-of-the-art α-particle detectors using GaN. Successful improvement in the growth of GaN drift layers (DL) with 2 order of magnitude lower in charge carrier density (CCD) (7.6 × <sup>10</sup><sup>14</sup>/cm3) on low threading dislocation density (3.1 × <sup>10</sup><sup>6</sup>/cm2) hydride vapor phase epitaxy (HVPE) grown free-standing GaN substrate, which helped ~3 orders of magnitude lower reverse leakage current (*IR*) with 3-times increase of reverse breakdown voltages. The highest reverse breakdown voltage of −2400 V was also realized from Schottky barrier diodes (SBDs) on a free-standing GaN substrate with 30 μm DL. The formation of thick depletion width (DW) with low CCD resulted in improving high-energy (5.48 MeV) α-particle detection with the charge collection efficiency (CCE) of 62% even at lower bias voltages (−20 V). The detectors also detected 5.48 MeV α-particle with CCE of 100% from SBDs with 30-μm DL at −750 V.

**Keywords:** GaN-on-GaN; schottky barrier diodes; high-energy α-particle detection; low voltage; thick depletion width detectors
