Ultrahigh Detectivity Broad Spectrum UV Photodetector with Rapid Response Speed Based on p‐β Ga₂O₃/n‐GaN Heterojunction Fabricated by a Reversed Substitution Doping Method

Abstract

An excellent broad‐spectrum (220–380 nm) UV photodetector, covering the UVA‐UVC wavelength range, with an ultrahigh detectivity of ≈1015 cm Hz1/2 W−1, is reported. It is based on a p‐β Ga2O3/n‐GaN heterojunction, in which p‐β Ga2O3 is synthesized by thermal oxidation of GaN and a heterostructure is constructed with the bottom n‐GaN. XRD shows the oxide layer is (−201) preferred oriented β‐phase Ga2O3 films. SIMS and XPS indicate that the residual N atoms as dopants remain in β Ga2O3. XPS also demonstrates that the Fermi level is 0.2 eV lower than the central level of the band gap, indicating that the dominant carriers are holes and the β Ga2O3 is p‐type conductive. Under a bias of −5 V, the photoresponsivity is 56 and 22 A W−1 for 255 and 360 nm, respectively. Correspondingly, the detectivities reach an ultrahigh value of 2.7 × 1015 cm Hz1/2 W−1 (255 nm) and 1.1 × 1015 cm Hz1/2 W−1 (360 nm). The high performance of this UV photodetector is attributed mainly to the continuous conduction band of the p‐β Ga2O3/n‐GaN heterojunction without a potential energy barrier, which is more helpful for photogenerated electron transport from the space charge region to the n‐type GaN layer.

Rapid Response Solar Blind Deep UV Photodetector with High Detectivity Based On Graphene:N/βGa2O3:N/GaN p‐i‐n Heterojunction Fabricated by a Reversed Substitution Growth Method

“…The band gap and Fermi levels of Ga 2 O 3 and GaN have been identified by transmittance and X-ray photoelectron spectroscopy (XPS) measurement, respectively. [52] For 𝛽Ga 2 O 3 here, the energy difference between the Fermi level and the valence band top is about 2.2 eV, indicating that the Fermi level is below the central level of the forbidden band, and the majority carriers in 𝛽Ga 2 O 3 are holes. This result is consistent with previous reports.…”

High-Performance Solar-Blind Ultraviolet Photodetectors Based on β-Ga2O3 Thin Films Grown on p-Si(111) Substrates with Improved Material Quality via an AlN Buffer Layer Introduced by Metal–Organic Chemical Vapor Deposition

“…It has been widely accepted that β-Ga 2 O 3 is one of the most promising materials for fabricating high-performance power devices. Another advantage of β-Ga 2 O 3 is its potential application in deep UV optoelectronic devices owing to its distinct absorption characteristics (absorption coefficient α > 10 5 /cm above the band edge of ∼4.5–5.0 eV) with a unique energy band gap structure. − Solar-blind deep UV photodetectors based on β-Ga 2 O 3 with ultrahigh responsivity ( R ) and detectivity ( D *) have been reported, with excellent detection capability and high D * values above 10 14 –10 15 cm·Hz 1/2 /W, − even higher than that of photomultiplier tubes. Furthermore, β-Ga 2 O 3 is suitable for wet chemical etching, which is particularly important for device design and fabrication, especially in large-scale production …”

“…Furthermore, β-Ga 2 O 3 is suitable for wet chemical etching, which is particularly important for device design and fabrication, especially in large-scale production. 11 A variety of epitaxial techniques have been employed to obtain high-quality β-Ga 2 O 3 thin films, including molecular beam epitaxy, 14 metal−organic chemical vapor deposition (MOCVD), 10 and pulsed laser deposition. 15 Intensive studies of β-Ga 2 O 3 thin-film growth have been carried out by using these epitaxial techniques.…”

Heteroepitaxial Growth of Single-Crystalline β-Ga2O3 on GaN/Al2O3 Using MOCVD

“…10−12 This p-GaN/n-Ga 2 O 3 heterojunction stack would be used for both optoelectronics and electronics. 13,14 To form a p-GaN/n-Ga 2 O 3 heterojunction, various methods have been conducted, including thermal oxidation, 15,16 pulse laser deposition (PLD), 12,17 sputtering, 18 and metalorganic chemical vapor deposition (MOCVD). 10 While thermal oxidation is an easy and cost-effective method for growing Ga 2 O 3 on top of GaN, the Ga 2 O 3 /GaN interface quality is poor, and the defects in the transition region would limit device performance.…”

“…The conductivity of UID n -type β-Ga 2 O 3 could be further enhanced by doping group IV elements (Si, Ge, and Sn), thus making it possible to obtain a highly conductive n -type β-Ga 2 O 3 . , To realize the full potential of Ga 2 O 3 -based applications, p -type Ga 2 O 3 is also required in addition to n -type Ga 2 O 3 because the p – n junction is an essential component for various devices. Unfortunately, both theoretical calculations and experimental results have showed that the formation of p -type Ga 2 O 3 has thus far been challenging. ,, Alternately, instead of employing homostructure p – n junctions made with both n -type and p -type Ga 2 O 3 semiconductors, heterojunctions of p -NiO/ n -Ga 2 O 3 or p -GaN/ n -Ga 2 O 3 have been proposed. − Recently, self-powered UVC photodetectors were reported from a p -GaN/ n -Ga 2 O 3 heterojunction with extremely high responsivity and a fast decay time. − This p -GaN/ n -Ga 2 O 3 heterojunction stack would be used for both optoelectronics and electronics. , …”