Heterojunction Diodes Research Articles

Theoretical study of a high-efficiency GaP–Si heterojunction betavoltaic cell compared with metal–Si Schottky barrier betavoltaic cell

In this work, energy converters, which contain a GaP–Si heterojunction and Si-based Schottky barrier diodes with Al, Ti, Ag, and W, are used to convert 2 μm-thick 63Ni radioactive source energy into electrical energy. First, energy deposition distributions of the 63Ni radioactive source in these converters are simulated by using the Monte Carlo method. Then, the electrical output properties of the 63Ni/GaP–Si cell and 63Ni/metal–Si cell are determined through the numerical calculation. For the 63Ni/GaP–Si cell, with the optimized thickness of the GaP layer and doping concentration of Si, the maximum output power density and the conversion efficiency are 0.189 µW cm−2 and 1.83%, respectively. For the Si-based Schottky barrier cells with Al, Ti, Ag, and W, the 63Ni/Al–Si cell has the best electrical output properties with the same thickness of the metal layer and doping concentration of Si. When the thickness of metal Al is 0.1 µm and the doping concentration Na is 1 × 1013 cm−3, the maximum output power density and the conversion efficiency are 0.121 µW cm−2 and 1.18%, respectively. The calculation results indicate that the 63Ni/GaP–Si battery has better electrical output properties than the 63Ni/Al–Si Schottky battery. These results are valuable for fabricating practical batteries.

Formation and Characterization of Ge1–x–ySixSny/Ge Heterojunction Structures for Photovoltaic Cell Application

Group-IV alloy semiconductor materials are much attractive for photovoltaic application, as those realizes multijunction photovoltaic with multi-heterostructure like group-III-V compound semiconductors [1]. In addition, group-IV alloy materials are expected to be familiar to Si integrated electronics. Ge1–x–ySixSny is one of candidate materials suitable for multijunction photovoltaic, since ternary alloy semiconductor provides energy band design independent on the lattice constant. The energy band gap of Ge1–x–ySixSny can be controlled from 0.66 eV to 1.0 eV with the epitaxial layer whose lattice is matching to Ge substrate.We previously reported the epitaxial growth of Ge1–x–ySixSny layers and also investigated the crystalline and electronic properties of them [2, 3]. However, the junction properties of Ge1–x–ySixSny/Ge heterostructure have not been well understood and it is necessary to clarify the crystalline and electronic properties of group-IV ternary alloy hetero junctions. In this study, we examined the crystal growth of pseudomorphic epitaxial layers of Ge1–x–ySixSny ternary alloy on Ge(001) substrates to form heterojunction structure for photovoltaic application. We also investigated the electronic and optoelectronic properties of these Ge1–x–ySixSny/n-Ge heterojunction diodes.Substrate used was n-type Ge(001) wafer. After chemical cleaning of substrate, a 200 nm-thick undoped Ge1–x–ySixSny layer was grown at 150–350 °C on substrate using molecular beam epitaxy system in ultrahigh vacuum chamber. Ge and Sn were deposited using Knudsen cells and Si was done using electron gun evaporation. Then, we prepared a mesa-shaped structure with wet etching. A 300 nm-thick SiO2 layer was deposited with coating of spin-on-glass and annealing at 450 °C. Finally, an Al electrode was prepared on contact holes to form heterojunction diode structure.We confirmed the crystalline structure of epitaxial layers with X-ray diffraction reciprocal space mapping. A Ge1–x–ySixSny layer with a high Sn content of 12% can be prepared with lattice matching epitaxy on Ge at a low temperature below 250 °C. It is also found that the small misfit between Ge1–x–ySixSny and Ge effectively impacts on the high crystalline quality and high thermal stability of substitutional Sn atoms in Ge matrix.Absorption spectroscopy and current-voltage characteristics of undoped Ge1–x–ySixSny/n-Ge heterojunction diodes were also performed. We observed good rectifying property of the diodes meaning that the majority carrier of these undoped Ge1–x–ySixSny ternary alloy layers is hole unintentionally generated due to defects. We also found the extension of the energy band gap of Ge1–x–ySixSny layer with Si and Sn contents. Photovoltaic property of Ge1–x–ySixSny/Ge heterojunction diodes were also measured. We can see the increasing of the open circuit voltage, Voc from 0.08 to 0.12 V for undoped Ge/n-Ge to undoped Ge0.54Si0.36Sn0.10/Ge heterojunction photovoltaic cell structure, which indicates the enhancement of Voc with increasing the energy bandgap of epitaxial layer. We also achieved the improvement of Voc by 0.14 V with 500 °C-annealing in hydrogen (H2) ambient, which suggests the annihilation or termination of point defect in the heterojunction structure.In conclusions, heterojunction structure with Ge1–x–ySixSny ternary alloy semiconductor layer provides the energy band engineering for photovoltaic applications. Understanding and controlling the defect properties in epitaxial growth and heterojunction formation should be key factors for the enhancement of performance of group-IV multijunction photovoltaic.

(Invited) Synthesis and Characterizations of Various Van Der Waals Hetero-Nanotubes Based on Single-Walled Carbon Nanotubes

We have successfully realized the synthesis of one-dimensional (1D) van der Waals heterostructures with single-walled carbon nanotube (SWCNT) as a template. A typical 1D heterostructure is composed of SWCNT, boron nitride nanotube (BNNT), and molybdenum disulfide nanotube (MoS2NT), coaxially grown by serial chemical vapor deposition (CVD) steps [1]. Isolated SWCNTs, BN-CVD at high temperatures such as 1100 °C from ammonia borane, and MoS2-CVD from MoO3 and Sulfur are original key requirements. Recently, we have achieved the additional CVD growth of carbon nanotubes from ethanol-CVD. We can remove SWCNT from SWCNT@BNNT by gentle oxidation process because BNNT is thermally more stable than SWCNT [2]. By comparing optical properties of BNNT@MoS2NT and SWCNT@BNNT@MoS2NT, we found the strong photoluminescence (PL) from monolayer MoS2NT of BNNT@MoS2NT and the exciton energy transfer between SWCNT and MoS2NT through thin BNNT for SWCNT@BNNT@MoS2NT [2]. We expect to prove the inter-tube excitons from the ultrafast optical spectroscopy [3]. We can realize various hetero-nanotubes in different morphologies such as SWCNT thin film, pillar-suspended SWCNT, chirality separated SWCNT deposited on TEM grid, and bulk SWCNTs grown on zeolite-supported catalysts [4]. Simply with SWCNT@BNNT in a thin film form, the enhanced thermal conductance [5] is very promising for macroscopic applications of heterostructures. Because BNNT coating over SWCNT film will not influence the transparency in the visible range, those films are immediately applicable for a saturable absorber in mode-lock fiber lasers. In order to fabricate a practical electronic or optoelectronics devices, micro-meter long 1D van der Waals heterostructure SWCNT@BNNT@MoS2NT were prepared between Si pillars. After transferring to SiO2 substrates and fabricating metal electrodes, we have examined various device characteristics. The naturally p-doped SWCNT and n-type MoS2NT becomes a radial semiconductor–insulator–semiconductor (S-I-S) heterojunction diode [6]. Optoelectronic and electronic properties of such devices will be discussed.Part of this work was supported by JSPS KAKENHI Grant Numbers JP18H05329, JP20H00220, and by JST, CREST Grant Number JPMJCR20B5, Japan.

(Invited) Hyperspectral Imaging of MoS2-hBN-Carbon Heteronanotubes: Novel Analytical Method with Optical Resolution of λ/3700

Low-dimensional nanostructures of electronic and/or optical materials possess a large number of new properties due to space quantization, thus exceeding the bulk “parent” materials. Similarly, nanoheterostructures of these materials provide even better control of properties and allow to explore new physics and utilize novel phenomena for device applications. In such systems, the materials properties can vary at the size scale of several nanometers.To meet the challenge of studying nanoheterostructures, the optical materials characterization tools have been recently extended beyond bulk spectroscopy or imaging. A number of Near-Field Optical Microscopy methods were developed. In this online presentation, we will report on a new approach to hyperspectral imaging with scattering Scanning Near-Field Optical Microscopy (sSNOM) which allowed us to perform materials spectroscopy with resolution not restricted by Abbe (diffraction) limit.In 2020, a new class of low-dimensional nanoheterostructure materials – two-dimensional sandwich materials (semiconductor and insulator van der Waals heterostructures) wrapped around carbon nanotube – has been synthesized [1]. Although confirmed by the structural studies (TEM) and elemental analysis (macro- to micro-scale), the heterostructures themselves or their devices were hardly imaged, except for AFM or SEM, not giving materials information. This is due to the diameter of the smallest part ca. 1-2 nm, much beyond the limitations of typical analytical methods.Here we present results on imaging different materials containing the nanoheterostructure with the sSNOM hyperspectral mapping [2]. The maximum resolution (imaging of 2 nm heteronanotube) achieved in these experiments exceeds the inverse wavelength of excitation mid-IR laser ~3,700 times, thus beating diffraction limits of regular optical spectroscopy. Heteronanotubes have been studied on the substrate as well as in real devices (diodes). Imaging of the heteronanotubes through the over-deposited metal electrodes was demonstrated.Acknowledgments: sSNOM work was supported by the National Science Foundation (Grant DMR-2011839). Part of this work was supported by JSPS KAKENHI Grant Numbers JP18H05329, JP20H00220, and by JST, CREST Grant Number JPMJCR20B5, Japan. Part of this work was conducted at Takeda Sentanchi Supercleanroom, supported by “Nanotechnology Platform” of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, Grant number JPMXP09F19UT0006.[1] Xiang, R.; Inoue, T.; Zheng, Y.; Kumamoto, A.; Qian, Y.; Sato, Y.; Liu, M.; Tang, D.; Gokhale, D.; Guo, J.; Hisama, K.; Yotsumoto, S.; Ogamoto, T.; Arai, H.; Kobayashi, Y.; Zhang, H.; Hou, B.; Anisimov, A.; Maruyama, M.; Miyata, Y.; Okada, S.; Chiashi, S.; Li, Y.; Kong, J.; Kauppinen, E. I.; Ikuhara, Y.; Suenaga, K.; Maruyama, S., One-dimensional van der Waals heterostructures. Science 2020, 367 (6477), 537.[2] Y. Feng, H. Li, T. Inoue, S. Chiashi, S. V. Rotkin, R. Xiang, and S. Maruyama, “One-dimensional van der waals hetero-junction diode”, (2020), arXiv:2012.03180.

Synthesis and characterization of layered Mo1-xErxS2 (0≤x≤0.05) nanostructures via 1,2-ethanediolmono(2-methylpropenoate) assisted microwave approach for gas detection

A series of layered Mo1-xErxS2 (0 ≤ x ≤ 0.05) nanosheets was prepared using a 1,2-ethanediolmono(2-methylpropenoate) assisted microwave approach. The influence of the Er-atoms on the structure, morphology, optical, and electrical properties of the MoS2 nanosheets was studied. The Mo1-xErxS2 (0 ≤ x ≤ 0.05) nanosheets were characterized using XRD, SEM, EDS, FTIR, Raman, and XPS measurements. The inclusion of the Er in Mo sites results in a decrease in the number of MoS2 layers and the widening of their lateral dimensions. The UV–vis spectrum of the Mo1-xErxS2 (0 ≤ x ≤ 0.05) 2D-layered nanostructures showed an increase of the optical bandgap and an enhancement of the direct exciton transitions at the K-points of the Brillouin zone. A heterojunction Mo1-xErxS2/p-Si diode was fabricated for the detection of gases. The developed heterojunction diode exhibited high sensitivity toward NO2 gas, under solar light illumination, with high stability and reproducibility.

A 3D SiC MOSFET with poly-silicon/SiC heterojunction diode

A three-dimensional (3D) silicon-carbide (SiC) trench metal–oxide–semiconductor field-effect transistor (MOSFET) with a heterojunction diode (HJD-TMOS) is proposed and studied in this work. The SiC MOSFET is characterized by an HJD which is partially embedded on one side of the gate. When the device is in the turn-on state, the body parasitic diode can be effectively controlled by the embedded HJD, the switching loss thus decreases for the device. Moreover, a highly-doped P+ layer is encircled the gate oxide on the same side as the HJD and under the gate oxide, which is used to lighten the electric field concentration and improve the reliability of gate oxide layer. Physical mechanism for the HJD-TMOS is analyzed. Comparing with the conventional device with the same level of on-resistance, the breakdown voltage of the HJD-TMOS is improved by 23.4%, and the miller charge and the switching loss decrease by 43.2% and 48.6%, respectively.

Characteristics and Electronic Band Alignment of a Transparent p-CuI/n-SiZnSnO Heterojunction Diode with a High Rectification Ratio.

Transparent p-CuI/n-SiZnSnO (SZTO) heterojunction diodes are successfully fabricated by thermal evaporation of a (111) oriented p-CuI polycrystalline film on top of an amorphous n-SZTO film grown by the RF magnetron sputtering method. A nitrogen annealing process reduces ionized impurity scattering dominantly incurred by Cu vacancy and structural defects at the grain boundaries in the CuI film to result in improved diode performance; the current rectification ratio estimated at ±2 V is enhanced from ≈106 to ≈107. Various diode parameters, including ideality factor, reverse saturation current, offset current, series resistance, and parallel resistance, are estimated based on the Shockley diode equation. An energy band diagram exhibiting the type-II band alignment is proposed to explain the diode characteristics. The present p-CuI/n-SZTO diode can be a promising building block for constructing useful optoelectronic components such as a light-emitting diode and a UV photodetector.

Solar cell operation of sputter-deposited n-BaSi2/p-Si heterojunction diodes and characterization of defects by deep-level transient spectroscopy

We form carbon-doped n-BaSi2(0.35 μm)/p-Si(111) heterojunction diodes by radio-frequency sputtering using BaSi2 and SiC targets, and demonstrate the solar cell operation for the first time under AM1.5 illumination. The electron trap level was measured to be 0.21 eV below the conduction band edge of the n-BaSi2 layers by deep-level transient spectroscopy. The shunt resistance reflecting the quality of the heterointerface exceeds 0.7 MΩ, one order of magnitude higher than that obtained for the same structure grown by molecular beam epitaxy. The carrier transport properties are discussed based on the external quantum efficiency spectrum and the band alignment.

Band alignment of wide bandgap NiO/MoO3 and NiO/WO3p-n heterojunctions studied by high-resolution X-ray photoelectron spectroscopy

NiO is one of the few transition metal oxides exhibiting p-type conductivity and visible light transparency. On the other hand, MoO3 and WO3 are high work function, wide gap metal oxides which show predominantly n-type character and have been widely applied in carrier selective contacts, heterojunction diodes, electrochromic and sensing applications. Hence, detailed understandings of the optical properties and electronic band offsets of the NiO/MoO3 and NiO/WO3p-n heterojunctions are crucial for the design and application of transparent oxide-based optoelectronic devices utilizing these heterojunctions. In this work, we synthesized thin films of the three oxides and characterized their structural and optical properties. In particular, the band alignment of NiO/MoO3 and NiO/WO3p-n heterojunctions were studied by high-resolution soft x-ray photoelectron spectroscopy (XPS). We found that both heterojunctions have a type-II band offset with the NiO/MoO3 exhibiting a larger valence band offset of 2.02 eV compared to 1.71 eV for NiO/WO3. The band positions of the three oxides with respect to the vacuum level obtained by Ultraviolet-Ambient Photoemission spectroscopy suggest that MoO3 and WO3 have a propensity to be n-type due to the easy formation of native donor defects. In contrast, NiO has a p-type character due to the high position of its VBM which favors the formation of native acceptor defects.

Fabrication and characterization of CuAlO2/ 4H–SiC heterostructure on 4H–SiC (0001)

In this work, CuAlO2 films were prepared on 4H–SiC (0001) using the sol-gel method. The surface morphology, structure and optical characteristics of the prepared films were studied. A homogeneous distribution of fine rhombohedral crystal structural grains is observed on the 4H–SiC substrate using scanning electron microscope (SEM). The film was confirmed to consist predominantly of delafossite CuAlO2 phase and impurity spinel CuAl2O4 phase via X-ray diffraction (XRD). The direct optical bandgap estimated from the measured transmittance spectra is approximately 3.85eV, while the indirect bandgap is 1.78 eV. Four emission peaks are observed in the photoluminescence (PL) spectra measured at room temperature. The emission peaks around 360 nm and 380 nm are the near band edge emission (NBE) of the prepared CuAlO2 films and the 4H–SiC substrate, respectively. The other two emission peaks around 410 nm and 470 nm arises from defects of Cu-vacancy. The fabricated p-CuAlO2/n-4H–SiC heterojunction diode exhibits typical rectification. Additionally, the turn-on voltage and rectification ratio at ± 3 V are determined to be 1.6 V and 1.26 × 103, respectively. A further 7.15 × 109 times increase of the hole injection capacity could be acquired potentially through an analysis of the energy band structure, which suggests that high injection capacity SiC bipolar devices could be feasibly achieved by utilizing CuAlO2 as the p + emitter.

An in-depth examination of opto-electrical properties of In-Yb2O3 thin films and fabricated Al/In-Yb2O3/p-Si (MIS) hetero junction diodes

An in-depth examination of opto-electrical properties of In-Yb2O3 thin films and fabricated Al/In-Yb2O3/p-Si (MIS) hetero junction diodes

Growth and characterization of low pressure chemical vapor deposited Si on Si-face 4H–SiC

Si/4H–SiC heterostructures are synthesized with low pressure chemical vapor deposition at temperatures ranging from 700 to 1080 °C. Microstructural investigations comprise scanning and transmission electron microscopy, as well as X-ray diffractometry analyses. The Si<111> and Si<110> growth orientations are found to be the most dominant, with a strong influence from the deposition temperature. Almost only Si<110> oriented and closed Si films are found at a deposition temperature of 900 °C. At the latter deposition temperature and above, the Si growth is heteroepitaxial. Heterojunction diodes by p+ and n+ doping of the Si top layer are fabricated and characterized. Strong Fermi level pinning is found to be responsible for deposition temperature dependent Schottky barrier heights.

Barrier height tuning by inverse sputter etching at poly-Si/4H-SiC heterojunction diodes

Si/4H-SiC heterojunction diodes (HJDs) are fabricated by applying Ar+ inverse sputter etching (ISE) of the 4H-SiC substrate prior to Si deposition. A subsequent annealing step was used to crystallize the sputter deposited amorphous Si. Numerical simulations and experiments were conducted to investigate the amorphization depth and etch rate of low energy Ar+ ions on the Si-face of 4H-SiC. Electrical characterization of the HJDs showed a strong influence of the ISE treatment in both n and p-type Si contacts compared to untreated diodes. The ISE power, as well as the ISE time can be tailored to adjust the Schottky barrier height (SBH) in a certain range, by simultaneously improving the device ideality for most ISE parameters compared to diodes without any ISE treatment. In addition, the homogeneity of the SBHs is improved, resulting in less variation over temperature and between different samples. The formation of a smooth Si–SiC transition region instead of a sharp interface is found after both ISE treatment and thermal annealing.

Temperature-dependent interface barrier behavior in MoS2/n-GaN 2D/3D heterojunction

We fabricated MoS2/n-type GaN 2D/3D heterojunction diode, investigated its structural properties and temperature-dependent current–voltage (I–V) characteristics. The MoS2 2D film on GaN is 5.2-nm-thick with ~ 0.64 nm interlayer distance. The Barrier height and ideality factor of the MoS2/n-type GaN heterojunction increase and decrease, respectively with rising temperature, associated with the barrier height inhomogeneities. The barrier height inhomogeneity evaluation considering the Gaussian distribution of barrier heights indicate the presence of double Gaussian barrier distribution with mean barrier heights of 0.95 and 1.44 eV and standard deviations of 0.11 and 0.18 eV in the temperature range of 125–225 and 225–400 K, respectively. Reverse current showed an electric field dependence with the carrier transport dominated by Poole-Frenkel emission irrespective of the temperature.

Electrical Properties of The Heterojunction Diode Produced Based on IGZO Thin Film

In this study, IGZO thin films were deposited on SLG and p-Si wafer at room temperature, under oxygen gas pressure of 5×10-2 and 7×10-2 mbar, using PLD technique and these thin films were annealed at 300oC temperature. IGZO thin films were grown in amorphous structure. As the oxygen gas pressure was increased, the particle size in the thin films were increased. IGZO/p-Si heterojunction diode was produced based on IGZO thin film that was grown at oxygen gas pressure of 7×10-2 mbar and not annealed, and J-V curves of this diode in darkness and under the illumination condition were obtained and then its ideality factor and barrier height were calculated. In an illumination condition, n,〖 R〗_s and Ф_b values of IGZO/Si heterojunction diode were calculated by the conventional J-V, Cheung Cheung and Norde methods. Results obtained in this work have been interpreted as well as concluded to be close to each other.

Electrical transport properties of thermally stable n-ZnO/AlN/p-Si diode grown using RF sputtering

The temperature dependent electrical transport properties of n-ZnO/AlN/p-Si heterojunction diode fabricated by RF sputtering system have been investigated over a wide temperature range of 303 K–413 K. The AlN buffer layer in-between ZnO and Si lowers the mismatch in thermal expansion coefficient/lattice constant for improved electrical and structural characteristics. XRD pattern and FESEM confirm the crystalline nature and good quality of ZnO thin film with uniform grain size and crack free structure respectively. As measured from the temperature dependent I–V curve, the apparent barrier height reduces as Ideality factor rises which shows good thermal stability within the temperature range studied here. The mean value of barrier height as well as the Richardson constant have been evaluated. Additionally, by taking into account the Gaussian distribution of inhomogeneous barrier heights, the modified Richardson constant has been estimated.

Near-white light-emitting diode from p-CuO/n-GaN heterojunction with an i-CuO electron blocking layer

• Near-white LED based on p-CuO/i-CuO/n-GaN was realized by magnetron sputtering and annealing treatment. • CuO could be used as hole injection layer and electron blocking layer under different annealing condition. • The chromaticity coordinates and related color temperatures of the devices were about (0.2381, 0.2606) and 22,505 K. • The i-CuO layer could improve the stability of electron injection and optimize the structure of diode. White light-emitting diodes (WLEDs) have advantages of high efficiency, energy saving, and long working-life, which are ideal choice for next generation of solid-state light sources. Herein we fabricated the near-white light-emitting diode based on the structure of p-CuO/i-CuO/n-GaN heterojunction by magnetron sputtering and annealing treatment. The surface morphology, crystal quality and electrical properties of the CuO layer were investigated by X-ray diffractometer, field emission-scanning electron microscope and Hall measurement. And the influence of the CuO electron blocking layer (EBL) on the diode characteristics were discussed. The current-voltage (I-V) characteristics of those diodes revealed typical p-n junction. Compared with p-CuO/n-GaN heterjunction diode, the EL spectrum of p-CuO/i-CuO/n-GaN heterjunction diode exhibited blue shift and higher intensity. It was found that the addition of CuO EBL enhanced the stability of the diode through analyzing the I-V and EL properties of the diodes. Moreover, at the injection current of 50 mA, the chromaticity coordinates of p-CuO/n-GaN and p-CuO/i-CuO/n-GaN heterojunction diodes are about (0.2686, 0.3334) and (0.2381, 0.2606), and the color temperature are 9205 K and 22,505 K, respectively. Eventually, the EL working mechanism of the two diodes was analyzed in the aspect of the energy band diagram. This study demonstrates the possibility of p-CuO/n-GaN heterojunction with an i-CuO electron blocking layer and their potentials for applications in WLEDs.

NIR self-powered photodetection and gate tunable rectification behavior in 2D GeSe/MoSe2 heterojunction diode

Two-dimensional (2D) heterostructure with atomically sharp interface holds promise for future electronics and optoelectronics because of their multi-functionalities. Here we demonstrate gate-tunable rectifying behavior and self-powered photovoltaic characteristics of novel p-GeSe/n-MoSe2 van der waal heterojunction (vdW HJ). A substantial increase in rectification behavior was observed when the devices were subjected to gate bias. The highest rectification of ~ 1 × 104 was obtained at Vg = − 40 V. Remarkable rectification behavior of the p-n diode is solely attributed to the sharp interface between metal and GeSe/MoSe2. The device exhibits a high photoresponse towards NIR (850 nm). A high photoresponsivity of 465 mAW−1, an excellent EQE of 670%, a fast rise time of 180 ms, and a decay time of 360 ms were obtained. Furthermore, the diode exhibits detectivity (D) of 7.3 × 109 Jones, the normalized photocurrent to the dark current ratio (NPDR) of 1.9 × 1010 W−1, and the noise equivalent power (NEP) of 1.22 × 10–13 WHz−1/2. The strong light-matter interaction stipulates that the GeSe/MoSe2 diode may open new realms in multi-functional electronics and optoelectronics applications.

Demonstration of n-Ga2O3/p-GaN Diodes by Wet-Etching Lift-Off and Transfer-Print Technique

In this letter, a 400-nm-thick $\beta $ -Ga2O3 nanomembrane is extracted from an n-Ga2O3-on-silicon wafer by wet etching, and then transferred to a p-GaN/ sapphire wafer by transfer-print technique to fabricate n-Ga2O3/p-GaN heterojunction diodes. X-ray photoelectron spectroscopy (XPS) measurement is used to accurately confirm that the valence-band offset of the heterojunction is 1.41± 0.07 eV. The diodes exhibit excellent electrical properties including high rectification ratio ( ${3.85}\times {10} ^{{6}}$ at ±5 V) and low reversed current density ( ${1.51}\times {10} ^{-{7}}\,\,\text{A}\cdot $ cm−2 at −5 V). The results show that the lift-off and transfer-print processes pave a new way for fabricating high-performance Ga2O3-based heterojunctions and bipolar devices.

A comprehensive study on effect of annealing on structural, morphological and optical properties of CdO and photodetection of heterojunction n-CdO/p-Si diode

The present investigation reports the synthesis of CdO using the facile sol-gel technique. The CdO samples exhibit cubic structure and their crystalline quality increases with different sintering temperatures (550, 650, and 750 °C). The maximum entropy method (MEM) was applied to calculate the charge density distribution of the CdO samples and the two-dimensional charge density maps showed a slight enlargement in the cell volume of the CdO with sintering temperatures. The bandgap of the CdO samples varied from 2.89 to 2.66 eV with increasing sintering temperature. Heterojunction n-CdO/p-Si photodiodes were constructed (using CdO samples) on silicon wafers using the spin coating procedure. The ideality factor of the diodes is found to decrease from 5.2 to 4.2 with sintering temperatures of the CdO. The heterojunction diode constructed using the CdO sample sintered at 750 °C exhibited the highest responsivity and external quantum efficiency values of 0.34 A/W and 109 %, respectively. Improved crystallinity, responsivity, and quantum efficiency make the developed CdO device useful for optoelectronics.