GaN Heterojunction Research Articles

Polarization-sensitive self-powered MoS2/a-GaN heterojunction photodetectors for ultraviolet polarized imaging

Polarization-sensitive self-powered MoS2/<i>a</i>-GaN heterojunction photodetectors for ultraviolet polarized imaging

DC and RF performance analysis of enhancement mode fin-shaped tri-gate AlGaN/GaN HEMT and MOSHEMT with ultra-thin barrier layer

The DC and RF assessment of critical barrier-AlGaN/GaN nano channel tri-gate fin-shaped High Electron Mobility Transistor (FinHEMT) is investigated for Enhancement-mode (E-mode) operation. We propose and analyze critical barrier layer (CBL) and critical-strained barrier layer (CSBL) FinHEMT for a fixed fin-shaped channel width (W fin = 160 nm) and height (H fin = 70 nm). The CBL FinHEMT ensures an E-mode operation by depleting two-dimensional electron gas (2DEG) near the channel region between AlGaN and GaN hetero-junction. The extracted threshold voltage (V T ) in CBL FinHEMT is 0.4 V as compared to −0.2 V obtained in CSBL FinHEMT. However, increased gate leakage current density and poor gate voltage swing in CBL FinHEMT is improved through a metal-oxide-semiconductor FinHEMT (FinMOSHEMT) structure by the incorporation of Al2O3 gate oxide layer between the tri-gate and CBL AlGaN layer. It results in a stable positive VT of 0.5 V due to the negatively charged Al2O3/barrier interface fixed charge density ( NAl2O3 ). The proposed CBL FinMOSHEMT has also been studied for different atomic layer deposition Al2O3 process-dependent variations in NAl2O3. The maximum on-state drain current and transconductance of 1.01 A mm−1 and 430 mS/mm have been extracted respectively with NAl2O3 of −9.2 × 1012 cm−2. Further, the RF analysis of the proposed CBL FinMOSHEMT structure with the same dimension exhibits improved f T and f max responses with 27 GHz and 90 GHz respectively over CBL FinHEMT. The results of the frequency responses obtained for the proposed design make it suitable for power electronics applications.

Demystifying metal-assisted chemical etching of GaN and related heterojunctions

GaN and related semiconductors have become an increasingly prominent material for a wide range of active and passive devices from optoelectronics to high frequency and power electronics as well as photocatalysis. Regardless of the application, anisotropic etching is required for micro and nano structuring, currently performed by reactive ion etching (RIE). Alternately, metal-assisted chemical etching (MacEtch) is an open-circuit plasma-free anisotropic etching method that has demonstrated high aspect ratio device structures devoid of plasma-induced damage found in RIE. This paper presents an in-depth study of the ensemble electrochemical mechanisms that govern the photo-enhanced MacEtch process of GaN and related heterojunctions. Through in-depth experimental investigations, modeling and simulations, the effects of local cathode and anode design, energy-band alignments, and solution chemistry on MacEtch are correlated with the underlying electronic mechanisms of carrier generation, annihilation, transport, and extraction, establishing a fundamental framework for parametrized prediction of system behavior. These findings carry profound implications for tailored design of photoelectrochemical processes employed not just for uniformly etching wide/ultrawide bandgap materials but more broadly for semiconductor-based photocatalytic reactions in general. One-pot photo-enhanced MacEtching of AlInGaN multi-heterojunction device structures including superlattices and multi-quantum wells are demonstrated.

Optimized 2D Bi[formula omitted]Se[formula omitted] thickness for broadband, high-performance, self-powered 2D/3D heterojunction photodetectors with multispectral imaging capability

The hybrid 2D/3D heterostructure, which synergistically combine the high surface area and superior surface properties of 2D materials with the volumetric advantages and mechanical stability of 3D materials, offer an efficient and unique platform for electronic, optoelectronic, and energy conversion applications. Although this structure offers numerous advantages, optimizing the performance of 2D/3D heterojunction devices still faces challenges such as interface control difficulty, doping uniformity, and scalability for mass production. To simplify and effectively optimize the performance of 2D/3D heterojunction devices, this study delves into the impact of the thickness of 2D Bi2Se3 films on the performance of Bi2Se3/GaN heterojunction photodetectors. In thinner Bi2Se3 films, a higher surface defect density increases carrier recombination efficiency, while in thicker films, an increase in internal defects impedes carrier transport. Our findings reveal an optimal film thickness that balances surface and internal defects, enhancing carrier dynamics and device performance. Remarkably, the Bi2Se3 (14.8 nm)/GaN heterojunction detector exhibits superior broadband response from ultraviolet to near-infrared, with a maximum responsivity of 0.07 A/W, a detectivity of 1.79 × 1012 Jones, and an on/off ratio of 1.02 × 104. Additionally, the device demonstrates prolonged stability in response and multispectral imaging capability. This research not only underscores the critical role of film thickness in modulating device performance but also provides novel theoretical and practical guidance for designing high-performance, self-powered, broadband heterojunction photodetectors, offering significant implications for scientific research and practical applications.

The determination of WSe2/GaN heterojunction band offsets in the semipolar (11–22) and nonpolar (11–20) planes by x-ray photoelectron spectroscopy

Wurtzite structured GaN has a severe polarization effect in the c (0001) plane, compared to which the polarization effect is small in the semipolar (11–22) plane, and there is no polarization effect in the nonpolar (11–20) plane GaN. To investigate the influence of the polarization effect on the band bending at the heterojunction interface, we fabricated tungsten diselenide (WSe2)/(0001) GaN, WSe2/(11–22) GaN, and WSe2/(11–20) GaN heterojunctions. We measured the heterojunction valence band offsets (VBOs) by x-ray photoelectron spectroscopy. The VBOs of the three WSe2/GaN heterojunctions were measured to be 2.43 ± 0.15, 2.51 ± 0.15, and 2.23 ± 0.15 eV, and the conduction band offsets were calculated to be 1.11 ± 0.15, 1.19 ± 0.15, and 0.91 ± 0.15 eV, showing the type II energy band alignment of the three heterojunctions. The results demonstrate that WSe2/(11–22) GaN-faced heterojunction band bending is the largest. This provides theoretical insights for two-dimensional WSe2 and three-dimensional semipolar (11–22) GaN and nonpolar (11–20) GaN heterojunction device preparation.

Vertical Van Der Waals Epitaxy of p‐MoxRe1‐Xs2 on GaN for Ultrahigh Detectivity Uv–vis–NIR Photodetector

Abstractvan der Waals (vdW) heterogeneous integration and doping engineering have emerged as crucial factors in advancing the development of functional device systems. This work presents a fully vertical 2D/3D vdW stacking p‐MoxRe1‐xS2/GaN (x = 0.10 ± 0.02) heterojunction photodetector, integrating multiple strategies for enhanced performance, such as mixed‐dimensional stacking, p‐type doping, vertical device design, and type‐II band alignment. By integrating horizontal, vertical, and quasi‐vertical devices on a Free‐standing (FS)‐GaN substrate, the vertical p‐MoxRe1‐xS2/GaN device demonstrates superior performance, including high Ilight/Idark ratio (1.48 × 106), large Responsivity (888.69 AW−1), high specific detectivity (D*) (6.13 × 1014 Jones), and fast response speed (rise/decay time of 181 ms/259 ms). Moreover, the spectral response encompasses the ultraviolet (UV), visible, and near‐infrared (NIR) regions through energy band integration and bandgap modulation. This design surpasses previous devices, highlighting the potential of highly sensitive and micro‐integrated optoelectronic devices enabled by vertical vdW heterogeneous integration.

Self-powered MoS2/n-type GaN heterojunction photodetector with broad spectral response in ultraviolet–visible–near-infrared range

Self-powered MoS2/n-type GaN heterojunction photodetector with broad spectral response in ultraviolet–visible–near-infrared range

Carrier transport across PtSe2/n-type GaN heterojunction

We fabricated PtSe2/n-type GaN heterojunction diode by transferring a large-scale grown two-dimensional (2D) PtSe2 layered film onto a 3D GaN substrate. The PtSe2 film transferred onto GaN was ∼5.84-nm thick and had 11 layers with interlayer spacing of 0.52 nm. An exploration of the temperature-dependence of the current–voltage (I–V) characteristics of the PtSe2/n-type GaN heterojunction in the range 125–400 K revealed a strong dependency of the ideality factor and barrier height on measurement temperature. This indicates a presence of low- and high-barrier-height patches resembling barrier inhomogeneities along the interface. A barrier inhomogeneity analysis with a consideration for the Gaussian barrier heights distribution demonstrated the existence of a double Gaussian barrier distribution having a mean barrier height of 0.97 and 1.41 eV in low- and high-temperature regimes, respectively. An examination of the temperature-dependency of reverse leakage current indicated the dominance of variable-range hopping conduction in lower temperature region (<225 K) and Poole–Frenkel emission mechanism in higher temperature region (>250 K). The interface state density Nss of the PtSe2/n-type GaN heterojunction determined from the capacitance method was lesser than that attained from the forward I–V characteristics that can be accredited to the inhomogeneous spreading of the Nss.

Fowler-Nordheim tunneling mechanism Graphene/GaN ultraviolet position-sensitive detector with high precision for optoelectronic demodulation applications

As an important component of optical sensors, position-sensitive detector (PSD) plays an important role in non-contact measurement systems and is widely used in many important fields. However, the preparation and application of ultraviolet (UV) PSD are still to be studied. Herein, we propose a high precision UV PSD constructed by graphene (Gr)/GaN heterojunction (active area is 5 ×5 mm2) for the first time, and Fowler-Nordheim tunneling mechanism has been used to improve device performance. Benefiting from the FNT, under a weak light power of 0.06 mW/cm2, the PSD is able to determine the position of the UV light spot through the output photocurrent difference, displays high precision (0.16 μA/mm), excellent weak light detection capability，and good linearity without power supply. Besides, the Gr/GaN show an ultralow threshold voltage (0.132 V) of FNT. When the bias is higher than 0.132 V, photogenerated carriers will tunneling the thin insulation layer by the FNT, resulting in a multiplication of the photocurrent. Therefore, under the same power densities light irradiation (0.06 mW/cm2), the device exhibits an ultrahigh responsivity of 1.88 A/W, a remarkable detectivity of 2.71 × 1013 Jones, and a high LDR of over 99.58 at 0 V bias. More importantly, as an optoelectronic demodulator the device realizes the decoding of optical signals into electrical signals, showing great potential for application in non-contact measurement systems.

Half‐Metallic Heusler Alloy/GaN Heterostructure for Semiconductor Spintronics Devices

AbstractBecause spin‐orbit coupling in wurtzite semiconductors is relatively weak compared with that in zincblende ones, the III‐nitride semiconductor GaN is a promising material for high‐performance optical semiconductor spintronic devices such as spin lasers. For the purpose of reducing the operating power of spin lasers, it is necessary to demonstrate highly efficient electrical spin injection from a ferromagnetic material into GaN with a low‐resistance contact. Here, an epitaxial half‐metallic Heusler alloy Co2FeAlxSi1−x(CFAS)/GaN heterostructure is developed by inserting an ultrathin Co layer between the CFAS and GaN. The CFAS/n+‐GaN heterojunctions clearly show tunnel conduction with very small rectification and a low resistance‐area product of ≈3.8 kΩµm2, which is several orders of magnitude smaller than those reported in previous work, at room temperature. Nonlocal spin signals and a Hanle effect curve are observed at low temperatures using lateral spin‐valve devices with the CFAS/n+‐GaN contacts, suggesting pure spin current transport in bulk GaN. The spin transport is observed at temperatures as high as room temperature, with a high spin polarization of 0.2 at a low bias voltage less than 2.0 V. This study is expected to open a path to GaN‐based spintronic devices with highly spin‐polarized and low‐resistance contacts.

High-performance self-powered ultraviolet photodetector in SnO2 microwire/p-GaN heterojunction using graphene as charge collection medium

• Using a facile vapor transport deposition method, the samples of SnO 2 microwires were synthesized individually self-catalyzed by a fast and simple CVD method. By combining p-type GaN substrate, a single SnO 2 microwire heterojunction photodetector working in the ultraviolet wavelengths was constructed. • By replacing the top electrodes from ITO to monolayer graphene, enhanced ultraviolet photoresponses were obtained, which exhibiting a peak responsivity 223.7 mA/W, detectivity ∼ 6.9 × 10 12 Jones, high EQE of 77%, and a fast response speed (rising/decaying times ∼ 18/580 μs) at 360 nm light illumination when the device is operated in self-driven mode. Our results suggest that the graphene transparent electrodes can not only allow the majority of the incident light to reach the contact area but also offer an easy carrier transport channel when the electron-holes were separated. • In particular, the microscopic photoresponse mechanism of the fabricated n-SnO 2 microwire/p-GaN heterojunction photodetector that using monolayer graphene as charge collection medium was studied. The Schottky-potential is formed by the built-in electric-field from graphene to the SnO 2 wire. The built-in field is in the same direction as the original SnO 2 /GaN built-in electric field, which was similar to the reverse voltage applied to the heterojunction. Therefore, the net built-in field toward the SnO 2 /GaN heterointerface can be increased, resulting in the increment of the carrier collection efficiency through graphene as a charge collection medium. Graphene monolayer has been extensively applied as a transparency electrode material in photoelectronic devices due to its high transmittance, high carrier mobility, and ultrafast carrier dynamics. In this study, a high-performance self-powered photodetector, which is made of a SnO 2 microwire, p-type GaN film, and monolayer graphene transparent electrode, was proposed and fabricated. The detector is sensitive to ultraviolet light signals and illustrates pronounced detection performances, including a peak responsivity ∼ 223.7 mA W –1 , a detectivity ∼ 6.9 × 10 12 Jones, fast response speed (rising/decaying times ∼ 18/580 μs), and excellent external quantum efficiency ∼ 77% at 360 nm light illumination without external power supply. Compared with the pristine SnO 2 /GaN photodetector using ITO electrode, the device performances of responsivity and detectivity are significantly increased over 6 × 10 3 % and 3 × 10 3 %, respectively. The performance-enhanced characteristics are mainly attributed to the high-quality heterointerface of n-SnO 2 /p-GaN, the highly conductive capacity, and the unique transparency of graphene electrodes. Particularly, the built-in potential formed at the SnO 2 /GaN heterojunction interface could be strengthened by the Schottky potential barrier derived from the graphene electrode and SnO 2 wire, enhancing the carrier collection efficiency through graphene as a charge collection medium. This work is of great importance and significance to developing excellent-performance ultraviolet photodetectors for photovoltaic and optoelectronic applications in a self-powered operation manner.

AlGaN/GaN‐Based Optoelectronic Synaptic Devices for Neuromorphic Computing

AbstractNeuromorphic computing promises to overcome the Von Neumann bottleneck of traditional computers. Optoelectronic synaptic devices are greatly desired given their potential applications in neuromorphic computing. In this work, optoelectronic synaptic devices with long‐term memory are fabricated. The devices are based on a GaN/AlGaN/AlN/GaN heterojunction and a SiNx charge trapping layer. Synaptic functionalities including excitatory postsynaptic current, paired pulse facilitation, and transition from short‐term memory to long‐term memory are realized. The retention time of long‐term memory may be more than 10 years, demonstrating the reliable charge storage of the devices. Logic functions are also realized by synergizing the photogating and electrical gating of the devices. The responsivity and specific detectivity are 2.64 × 105 A W−1 and 1.79 × 1016 Jones at the optical power density of 1.4 mW cm−2, respectively. In addition, the devices have a reconfigurable switch of 1000 cycles with working temperature up to 200 °C.

Bias Current Modulation of DC and RF Properties of AlmGa1‐m∼GaN Heterojunction IMPATT at Sub‐Millimeter Wave Frequency

AbstractLarge signal RF properties of double drift region (DDR) Impact Avalanche Transit Time (IMPATT) device based on AlmGa1‐m∼GaN heterojunction (HT) are investigated and their variation with bias currents has been presented here. These RF properties and their modulation will significantly validate the acceptability of the particular HT in the sub‐millimeter wave frequency domain. Avalanche noise plays the prime ground for making the IMPATT diode basically noisy and tunneling decays the performance of the device, as we move towards the higher frequency range like the sub‐millimeter frequency. These setbacks can be done with if the homojunction (HM) is replaced by heterojunction. This authenticates the choice of heterojunction over homojunction. Here, the author takes 500 GHz as the frequency of concern in the sub‐millimeter wave range. Here, two complementary heterojunctions of AlmGa1‐m∼GaN is taken with m = 0.4 or the mole fraction of Al in the alloy being 40% and their RF results are compared with two homojunctions of GaN and AlGaN for double drift region (DDR) IMPATT diode. Outcomes indicate that HT diodes surpass the high‐frequency performance of HM diodes if compared on the basis of dc to RF conversion efficiency and output power due to the influence of large amplitude ac signal. It is also observed that with increasing bias voltage dependent current, which is varied from 20 × 108to 40 × 108Am−2, the efficiency of conversion together with the power output increases. These results will be very important for further research in this domain.

Self-powered broadband photodetection enabled by facile CVD-grown MoS2/GaN heterostructures.

Achieving self-powered photodetection without biasing is a notable challenge for photodetectors. In this work, we demonstrate the successful fabrication of large-scale van der Waals epitaxial molybdenum disulfide (MoS2) on a p-GaN/sapphire substrate using a straightforward chemical vapor deposition (CVD) technique. Our research primarily centers on the characterization of these photodetectors produced through this method. The MoS2/GaN heterojunction photodetector showcases a broad and extensive photoresponse spanning from ultraviolet A (UVA) to near-infrared (NIR). When illuminated by a 532 nm laser, its self-powered photoresponse is characterized by a rise time (τr) of ∼18.5 ms and a decay time (τd) of ∼123.2 ms. The photodetector achieves a responsivity (R) of ∼0.13 A W-1 and a specific detectivity (D*) of ∼3.8 × 1010 Jones at zero bias. Additionally, while utilizing a 404 nm laser, the photodetector reaches a maximum R and D* of ∼1.7 × 104 A/W and ∼1.6 × 1013 Jones, respectively, at Vb = 5 V. The operational mechanism of the device can be explained by the diode characteristics involving a tunneling current in the presence of reverse bias. The exceptional performance of these photodetectors can be attributed to the pristine interface between the CVD-grown MoS2 and GaN, providing an impeccably clean tunneling surface. Additionally, our investigation has unveiled that MoS2/GaN heterostructure photodetectors, featuring MoS2 coverage percentages spanning from 20% to 50%, exhibit improved responsivity capabilities at an external bias voltage. As a result, this facile CVD growth technique for MoS2 photodetectors holds significant potential for large-scale production in the manufacturing industry.

Numerical study and design of high-efficiency p-In0.1Ga0.9N/i-GaN/n-GaN heterojunction photodiode

This paper reports the performance of a proposed GaN heterojunction p-i-n photodiode with a p-type In0.1Ga0.9N layer. The simulation results show that, compared with the GaN homojunction p-i-n structure, the GaN heterojunction p-i-n structure performs better on the basis of such simulations as photocurrent density and responsivity. The effects of reverse bias voltage, light intensity and i-GaN absorbing layer thickness are explored. The peak responsivity and the cutoff frequency are found to increase remarkably with increasing reverse bias voltage. The degradation of device responsivity and cutoff frequency at high optical excitation power density are also investigated. By increasing the i-GaN absorbing layer thickness, responsivity increases but cutoff frequency decreases. The maximum responsivity is 0.3 A/W at 0.363 μm under an illumination intensity of 105 W/cm2 and an applied reverse bias voltage of −2 V, while the highest cutoff frequency 12 GHz is achieved at an applied reverse bias voltage of −14 V.

Heteroepitaxial growth and band alignment of β-Ga2O3 on GaN substrate grown by non-vacuum mist-CVD

Recently, Ga2O3 has attracted widespread attention from domestic and foreign research scholars due to its large bandgap and high breakdown electric field. And it has huge application prospects in many fields such as optoelectronic devices, transistors, and high-power devices. Different from the traditional expensive and complex methods such as PLD, MOCVD, and MBE to epitaxially grow the Ga2O3 films, the low-cost, non-vacuum, easy-to-operate mist-CVD method has been focused. In this work, (2‾01) β-Ga2O3 has been heterogeneously grown on (0001) GaN. According to AFM and XPS results, the RMS of β-Ga2O3 thin films is 4.05 nm, the conduction band excursion ΔEC of the band alignment of β-Ga2O3/GaN is 1.26 eV, the valence band excursion ΔEV is 0.4 eV, and then the band alignment of β-Ga2O3/GaN heterojunction is obtained. These results prove the application potential of β-Ga2O3/GaN heterojunction in devices and the huge advantages and future development potential of the mist-CVD method.

Effect of uniaxial compressive stress with different orientations on the hole mobility of wurtzite GaN heterojunction quantum well

The influence of uniaxial compressive stress with different orientations to the current channel on the physical and transport properties of the wurtzite GaN heterojunction quantum well is investigated in this work. By using the six-band stress-dependent k × p Hamiltonian, accurate two-dimensional physical pictures are given for the quantized valence subband under the uniaxial compressive stress on the (0001) transport plane. The low-field hole mobility is obtained by the Kubo–Greenwood formula, taking the scattering rates for acoustic phonon, polar optical phonon, and surface roughness into account. Using these methods, the microscopic relationship between the orientation of uniaxial compressive stress and low-field hole mobility is obtained according to the variations of valence subband dispersion and hole effective mass. Results show that for temperatures around and above room temperature, the acoustic phonon scattering is predominant. We find that the mobility gain is mostly contributed from effective mass, and there is an increasing trend under uniaxial compressive stress with all orientations due to the effective mass reduction. For the same stress value, the mobility decreases monotonically as the stress orientation changes from 0° to 90° with respect to the current channel. At room temperature, the calculated low-field hole mobility is 182 cm2/V s under 8 GPa uniaxial compressive stress parallel to the current channel, with the hole density of 5.5 × 1013 cm−2 and the effective electric field of 0.93 MV/cm.

The same band alignment of two hybrid 2D/3D vertical heterojunctions formed by combining monolayer MoS2 with semi-polar (11–22) GaN and c-plane (0001) GaN

Traditional c-plane (0001) GaN based devices are subject to a strong polarization field at the hetero-interfaces which handicaps the performance of photoelectric devices. However, the semi-polar (11–22) GaN has great potential for reducing the polarization effects compared with c-plane (0001) GaN. Here, we have fabricated MoS2/(11–22) GaN heterojunction and determined the band alignment by X-ray photoelectron spectroscopy (XPS). For comparison, the band alignment of MoS2/(0001) GaN heterojunction has also been measured to explore the influence of GaN with different crystal orientations on the energy band of MoS2/GaN heterojunction. Surprisingly, the band alignments of the two MoS2/GaN heterojunctions are the same, which could be caused by the unsaturated and omnidirectional properties of van der Waals forces at the interface of MoS2 and GaN. The measurement result of the valence band offsets (VBOs) of the two MoS2/GaN heterojunctions is 1.54 ± 0.15 eV. And the conduction band offsets (CBOs) are determined to be 0.29 ± 0.15 eV, revealing type-II band alignments of the two heterojunctions. We have also confirmed the number of MoS2 layers on the MoS2/GaN heterojunctions by Raman spectroscopy and the orientations of the GaN substrates by X-ray diffraction. The determination of band alignments between two-dimensional (2D) MoS2 and three-dimensional (3D) semi-polar (11–22) GaN opens up a way for modeling and designing high performance photoelectric devices based on hybrid MoS2/semi-polar GaN heterojunctions.

Achieving highly-efficient H2S gas sensor by flower-like SnO2–SnO/porous GaN heterojunction

A flower-like SnO2–SnO/porous GaN (FSS/PGaN) heterojunction was fabricated for the first time via a facile spraying process, and the whole process also involved hydrothermal preparation of FSS and electrochemical wet etching of GaN, and SnO2–SnO composites with p–n junctions were loaded onto PGaN surface directly applied to H2S sensor. Meanwhile, the excellent transport capability of heterojunction between FSS and PGaN facilitates electron transfer, that is, a response time as short as 65 s and a release time up to 27 s can be achieved merely at 150 °C under 50 ppm H2S concentration, which has laid a reasonable theoretical and experimental foundation for the subsequent PGaN-based heterojunction gas sensor. The lowering working temperature and high sensitivity (23.5 at 200 ppm H2S) are attributed to the structure of PGaN itself and the heterojunction between SnO2–SnO and PGaN. In addition, the as-obtained sensor showed ultra-high test stability. The simple design strategy of FSS/PGaN-based H2S sensor highlights its potential in various applications.

Significant performance improvement of AlGaN solar-blind heterojunction phototransistors by using Na2S solution based surface treatment

Deep ultraviolet (DUV) photodetectors are of tremendous interest in applications requiring solar-blind sensing. Here, solar-blind Al0.5GaN/Al0.4GaN heterojunction phototransistors with significantly improved performance have been fabricated using Na2S solution based surface treatment. Compared with the usual (NH4)2S-based treatment, the dark current of the HPTs fabricated with Na2S-based treatment is reduced by more than an order of magnitude, and the optical gain is increased from 2.6 × 102 to 9.6 × 103. A high photo to dark current ratio of more than four orders of magnitude was obtained at zero bias and is higher than two orders of magnitude in the whole measuring bias range. Characterizations on the surface morphology, optical properties, surface chemical bonding states, and surface potential reveal that the Na2S-based solution is very effective in removing III-oxides, reducing the deep-level defects associated with VIII, and thus forming SN donors on the dry-etched and thermally-annealed n-AlGaN layer. As a result, the Ohmic contact properties of the HPTs are significantly, contributing to the photoresponse enhancement. Moreover, the surface leakage is suppressed by the reduction of deep-level acceptors, thereby improving the electron injection and optical gain of the HPTs.