High Acceptor Concentrations Research Articles

Mg activation anneal of the p-GaN body in trench gate MOSFETs and its effect on channel mobility and threshold voltage stability

This work addresses the impact of the Mg activation anneal step and the resulting acceptor concentration on the channel mobility and VT stability of vertical MOSFETs. Increasing the annealing time with N2 only ambient and the annealing temperature with O2 in the ambient is shown to be effective in increasing the channel acceptor concentration. When the effective acceptor concentration is increased, the mobility is degraded due to a transition in the main scattering mechanism from Coulomb to surface roughness scattering. Degradation of the on-state current and maximum transconductance at high operating temperatures was linked to bulk mobility degradation of the drift layer due to lattice scattering. The two Mg activation annealing conditions considered here show different trends with regard to the threshold voltage stability, while N2 only ambient did not impact this parameter, including O2 increased threshold voltage instability. It is shown that increasing the Mg chemical concentration in the p-GaN layer degrades channel mobility and threshold voltage stability, irrespectively of the effective acceptor concentration, providing evidence for degradation of the channel/dielectric interface characteristics with higher Mg chemical concentration. This study shows that it is possible to achieve very low threshold voltage hysteresis and high channel mobility by reducing the Mg chemical concentration while maintaining high effective acceptor concentration. These results provide key insights for the development of vertical GaN FETs.

Controlling Electron/Hole Recombination in Near-Infrared Polymer Phototransistors through an Insulation Medium: A Pathway to Ultrahigh Photosensitivity.

In near-infrared (NIR) polymer phototransistors, the photoresponse is proportional to the turn-on voltage shift (ΔVth). Due to the narrow band gap of NIR polymers, the ΔVth value is usually small. However, the use of a single bulk heterojunction (BHJ) layer has a minimal effect on increasing the value of ΔVth. This is because doping with high concentrations of acceptors results in strong current traps and accelerates electron/hole recombination. In this work, a new strategy is proposed to control the recombination of electrons/holes. By doping an insulating medium made of polystyrene (PS) into BHJs, PC61BM:PS:PDPP3T-based ternary NIR phototransistors with high acceptor concentrations were prepared by using a one-step film transfer method (FTM). Compared with a PC61BM:PDPP3T-based binary device (1:1), a ternary device (1:1:1) exhibited a significant performance improvement. The ΔVth value (∼29.5 ± 1.0 V) increased by approximately 4-fold, the Iph/Idark (∼4.4 × 106) increased by a factor of 3000 to 4000-fold, and the dark current decreased by 2-3 orders of magnitude (@ Vg = 0 V). Additionally, the ternary devices demonstrated excellent performance across a wide ternary ratio range (1:1:1 to 4:2:1).

Lasing in Zn-doped GaAs nanowires on an iron film

In this work, we demonstrate optically pumped lasing in highly Zn-doped GaAs nanowires (NWs) lying on an iron film. The conically shaped NWs are first covered with an 8 nm thick Al2O3 film to prevent atmospheric oxidation and mitigate band-bending effects. Multimode and single-mode lasing have been observed for NWs with a length greater or smaller than 2 μm, respectively. Finite difference time domain calculations reveal a weak electric field enhancement in the Al2O3 layer at the NW/iron film interface for the lasing modes. The high Zn acceptor concentration in the NWs provides enhanced radiative efficiency and enables lasing on the iron film despite plasmonic losses. Our results open avenues for integrating NW lasers on ferromagnetic substrates to achieve new functionalities, such as magnetic field-induced modulation.

Charge Control in Schottky-Type p-GaN Gate HEMTs With Partially and Fully Depleted p-GaN Conditions

The Schotty-type p-GaN gate high-electron-mobility transistors (HEMT) feature a unique gate structure. A comprehensive understanding of the charge control mechanism in the p-GaN gate region is a fundamental step for the optimization of this technology. In this work, a physics-based analytical model is presented which takes into consideration all the capacitive effects from gate metal deep into the GaN buffer. According to our analysis, the p-GaN layer can be either partially depleted by the metal/p-GaN Schottky junction or fully depleted, depending on the doping concentration and thickness of the p-GaN layer. Our model accurately captures the charge control properties under both conditions and is validated against TCAD numerical simulations. For a certain p-GaN thickness, a lightly doped p-GaN leads to a full-depletion condition, such that the acceptor concentration directly affects the band diagram at AlGaN/GaN interface. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> of the HEMT increases quickly with acceptor concentration in p-GaN. With sufficiently high acceptor concentration in p-GaN, the device reaches the partial-depletion condition, the acceptor concentration loses its influence over the band diagram at the location of the AlGaN/GaN interface, since the Fermi-level at the AlGaN surface is pinned near the valence band of p-GaN. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> starts to decrease with acceptor concentration, but at a relatively slow rate. The maximum <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> is obtained near the boundary between partial-and full-depletion conditions. In consideration of the process margin, the device designed with a partially depleted p-GaN is preferable, since it ameliorated the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> sensibility against acceptor concentration.

Resonance Energy Transfer to Track the Motion of Lanthanide Ions-What Drives the Intermixing in Core-Shell Upconverting Nanoparticles?

The imagination of clearly separated core-shell structures is already outdated by the fact, that the nanoparticle core-shell structures remain in terms of efficiency behind their respective bulk material due to intermixing between core and shell dopant ions. In order to optimize the photoluminescence of core-shell UCNP the intermixing should be as small as possible and therefore, key parameters of this process need to be identified. In the present work the Ln(III) ion migration in the host lattices NaYF4 and NaGdF4 was monitored. These investigations have been performed by laser spectroscopy with help of lanthanide resonance energy transfer (LRET) between Eu(III) as donor and Pr(III) or Nd(III) as acceptor. The LRET is evaluated based on the Förster theory. The findings corroborate the literature and point out the migration of ions in the host lattices. Based on the introduced LRET model, the acceptor concentration in the surrounding of one donor depends clearly on the design of the applied core-shell-shell nanoparticles. In general, thinner intermediate insulating shells lead to higher acceptor concentration, stronger quenching of the Eu(III) donor and subsequently stronger sensitization of the Pr(III) or the Nd(III) acceptors. The choice of the host lattice as well as of the synthesis temperature are parameters to be considered for the intermixing process.

Effect of Diffusion on Photo-Induced Excited-State Energy Transfer between Fluorescent Semiconducting Molecules: Tris-(8-hydroxyquinoline) Aluminum and 6,13-Bis (Triisopropylsilylethynyl) Pentacene

In the present work, the effect of diffusion on photo-induced excitation energy transfer between fluorescent organic semiconducting molecules tris-(8-hydroxyquinoline) aluminum (AlQ3, n-type donor) and 6,13-bis (triisopropylsilylethynyl) pentacene (TIPS-P, p-type acceptor) at a concentration range of 10–4 to 10–6 M in chloroform solution was studied by steady-state and time-domain fluorescence measurements. The donor–donor interaction strength is significantly weaker than the donor–acceptor strength (the ratio of donor–donor to donor–acceptor interaction strengths is 1.55 × 103) in chloroform solution. Considerable overlap between donor emission and acceptor absorption and high interaction parameters favors direct Förster energy transfer and exciplex (D*A) formation. Excitation energy migration does not take place between donor molecules. However, material diffusion appears to influence the donor decay dynamics by forming charge-transfer exciplex complexes and modulating the excitation energy transfer rate from the metal-to-ligand charge-transfer (MLCT) state of the donor to vibronic states of the acceptor at a low acceptor concentration. At high acceptor concentrations, energy transfer from the excited donor to acceptor occurs through the exchange mechanism along with Förster long-range dipole–dipole interactions, and the corresponding critical transfer distance is found to be ∼42 Å. A blue-shift in AlQ3 emission, a red-shift in the 0–0 vibronic peak of TIPS-P, and quenching of exciplex decay following Stern–Volmer quenching are observed, with the increase in acceptor concentration. No evidence of excimer formation is observed in acceptor molecules.

Neutron irradiation induced defects in oxides and their impact on the oxide properties

Understanding the irradiation-induced defects in oxides is of interest for a wide range of applications. ZnO is an interesting oxide with mixed ionic and covalent bonding that contains a variety of point defect structures—making it an excellent model for studying irradiation-induced defects and their impact on properties. Here, we investigate the effects of neutron irradiation on the formation of defects and on the structural, optical, and electrical properties of ZnO single crystals. We observe the formation of vacancies and voids via positron annihilation spectroscopy. Neutron irradiation led to a significant deterioration of the ZnO structure and formed a high concentration of point defects, vacancy clusters, and voids with large disparities in their structure across variable irradiation times. It also led to significant changes in the optical properties and sample color. Irradiation for 444 h induced a high concentration of Cu acceptors as well as a high concentration of Ga donors. Temperature-dependent Hall effect measurements revealed the competing production of donors and acceptors and showed an increase in the slope of the carrier freeze-out curve with increasing irradiation dose. This work demonstrates the combined effects of neutron irradiation in producing a wide range of structural defects, impurities, and dopants in oxides and their enormous impact on modifying the oxide structure and both the optical and electronic properties. It particularly emphasizes the importance of considering the production of new impurities and dopants during the neutron irradiation of oxides.

Modeling current transport in boron-doped diamond at high electric fields including self-heating effect

In this work, current multiplication at high electric field in epitaxial boron-doped diamond with high acceptor concentration is analyzed, including self-heating effect and impurity impact ionization. Quasi-static current-voltage (I-V) characteristics were measured using a transmission-line pulse setup with 100 ns pulse duration on samples with two Ohmic titanium/gold electrodes. Unambiguous exponential and super-exponential behaviors are observed in the I-V curves along with, in some cases, negative differential resistance. The self-heating effect is analyzed using transient interferometric mapping of the thermal energy distribution between electrodes with a ns time scale. Measured I-V characteristics are modeled by finite element method and by considering boron acceptor ionization due to self-heating effect and impurity impact ionization. Simulated I-V characteristics, in particular the appearance of the negative differential resistance region attributed to self-heating, are in good agreement with experimental data.

Theoretical analysis of doping concentration, layer thickness and barrier height effects on BaSi2 based homojunction solar cells toward high efficiency

Numerical calculation and theoretical study on high optical absorption material BaSi2 based np or nip homojunction solar cells were conducted by using AMPS software. The effects of doping concentration and front layer thickness on the performance of n-BaSi2/p-BaSi2 homojunciton solar cell were comprehensive investigated. It was found that the donor concentration and thickness of n-BaSi2 had decisive influence on the light performance of n-BaSi2/p-BaSi2 homojunciton solar cell, since high donor concentration in n-BaSi2 gave rise to extremely high hole trapping concentration in n-BaSi2 and thus reduced the hole current as well as total current density under light illumination. Consequently, the n-BaSi2 layer was suggested to be designed either with low donor concentration or with thin thickness to achieve high power conversion efficiency. Same effect of n-BaSi2 on the performance of nip homojucntion solar cell was also observed. Contrarily, the optimized p-BaSi2 was suggested to possess high acceptor concentration and to be slightly thicker, in order to maintain the high built-in potential as well as Voc of nip homojunciton solar cell. On account of the front and rear contact barrier height between electrode and BaSi2 functional layer, the barrier height between p-BaSi2 and rear contact electrode had comparably more sensitive influence to attenuate the built-in potential and thus the Voc of BaSi2 based nip the solar cell. However, this negative influence caused by high barrier height could be convincingly conquered by employing thick p-BaSi2 layer.

Low VF 4H-SiC N-i-P diodes using newly developed low-resistivity p-type substrates

We fabricated 4H-SiC N-i-P (N-intrinsic-P) diodes using newly developed low-resistivity p-type substrates with higher acceptor concentrations than conventional substrate. N-i-P diodes with 10 μm thick n− drift layers were fabricated on both a low-resistivity p-type substrate and a conventional one to investigate the difference in substrate resistance and bipolar degradation with a heavily doped p-type buffer layer. The differential on-resistance of N-i-P diode, using low-resistivity p-type substrates was decreased to one third compared to the conventional case, and the difference was similar to the p-type substrates resistivity. No stacking faults expansion was observed up to 1100 A cm−2. N-i-P diodes with 233 μm thick n− drift layers were fabricated to demonstrate forward characteristics instead of an ultra-high voltage n-channel IGBTs. The forward characteristics of the N-i-P diodes with 233 μm thick n− drift layers at 200 °C showed low on-voltage 6.9 V and low differential on-resistance 32.2 mΩ cm2.

Potassium-Presenting Zinc Oxide Surfaces Induce Vertical Phase Separation in Fullerene-Free Organic Photovoltaics.

Bulk heterojunction (BHJ) structure based organic photovoltaics (OPVs) have recently showed great potential for achieving high power conversion efficiencies (PCEs). An ideal BHJ structure would feature large donor/acceptor interfacial areas for efficient exciton dissociation and gradient distributions with high donor and acceptor concentrations near the anode and cathode, respectively, for efficient charge extraction. However, the random mixing of donors and acceptors in the BHJ often suffers the severe charge recombination in the interface, resulting in poor charge extraction. Herein, we propose a new approach-treating the surface of the zinc oxide (ZnO) as an electron transport layer with potassium hydroxide-to induce vertical phase separation of an active layer incorporating the nonfullerene acceptor IT-4F. Density functional theory calculations suggested that the binding energy difference between IT-4F and the PBDB-T-2Cl, to the potassium (K)-presenting ZnO interface, is twice as strong as that for IT-4F and PBDB-T-2Cl to the untreated ZnO surface, such that it would induce more IT-4F moving toward the K-presenting ZnO interface than the untreated ZnO interface thermodynamically. Benefiting from efficient charge extraction, the best PCEs increased to 12.8% from 11.8% for PBDB-T-2Cl:IT-4F-based devices, to 12.6% from 11.6% for PBDB-T-2Cl:Y1-4F-based devices, to 13.5% from 12.2% for PBDB-T-2Cl:Y6-based devices, and to 15.7% from 15.1% for PM6:Y6-based devices.

Hierarchy of domain reconstruction processes due to charged defect migration in acceptor doped ferroelectrics

Evolution of a stripe array of polarization domains triggered by the oxygen vacancy migration in an acceptor doped ferroelectric is investigated in a self-consistent manner. A comprehensive model based on the Landau–Ginzburg–Devonshire approach includes semiconductor features due to the presence of electrons and holes, and effects of electrostriction and flexoelectricity especially significant near the free surface and domain walls. A domain array spontaneously formed in the absence of an external field is shown to undergo a reconstruction in the course of the gradual oxygen vacancy migration driven by the depolarization fields. The charge defect accumulation near the free ferroelectric surface causes a series of phenomena: (i) symmetry breaking between the positive and negative c-domains, (ii) appearance of an effective dipole layer at the free surface followed by the formation of a surface electrostatic potential, (iii) tilting and recharging of the domain walls, especially pronounced at higher acceptor concentrations. An internal bias field determined by the gain in the free energy of the structure exhibits dependences of its amplitude on time and dopant concentration well comparable with available experimental results on aging in BaTiO3.

Towards high efficiency inverted Sb2Se3 thin film solar cells

Sb2Se3 as a rising star semiconducting material with a bandgap of 1.1 eV has played a role of the absorber in the thin film solar cells. Regular device architectures such as metal grids/buffer/Sb2Se3/metal electrode, or transparent electrode film/buffer/Sb2Se3/metal electrode have been fabricated both experimentally and theoretically and exhibit relatively good photovoltaic performances. Yet the theoretical power-conversion efficiency is not competitive with commercial thin film solar cells. Therefore, we propose an inverted architecture with top illumination through ITO substrate, with allocating the hole transport layer (HTL) on top of Sb2Se3 and stacking electron transport layer beneath the Sb2Se3. Indeed an optimal power conversion efficiency of 24.7% and fill factor of 80.3% have been simulated in the solar devices with the selected NiO as the HTL. The improvement in solar cell performances stems from the satisfying bandgap alignment and improved hole conductivity due to the high acceptor concentration of the chosen material. Further increase of the device performances depend on the high quality Sb2Se3 thin films, i.e., with negligible defects states and the suppression of defects at the Sb2Se3/HTL interfaces.

Study of thin film poly-crystalline CdTe solar cells presenting high acceptor concentrations achieved by in-situ arsenic doping

Doping of CdTe using Group-V elements (As, P, and Sb) has gained interest in pursuit of increasing the cell voltage of CdTe thin film solar devices. Studies on bulk CdTe crystals have shown that much higher acceptor concentration than the traditional copper treatment is possible with As, P or Sb, enabled by high process temperature and/or rapid thermal quenching under Cd overpressure. We report a comprehensive study on in-situ As doping of poly-crystalline CdTe solar cells by MOCVD, whereby high acceptor densities, approaching 3 × 1016 cm−3 were achieved at low growth temperature of 390 °C. No As segregation could be detected at grain boundaries, even for 1019 As cm−3. A shallow acceptor level (+0.1 eV) due to AsTe substitutional doping and deep-level defects were observed at elevated As concentrations. Devices with variable As doping were analysed. Narrowing of the depletion layer, enhancement of bulk recombination, and reduction in device current and red response, albeit a small near infrared gain due to optical gap reduction, were observed at high concentrations. Device modelling indicated that the properties of the n-type window layer and associated interfacial recombination velocity are highly critical when the absorber doping is relatively high, demonstrating a route for obtaining high cell voltage.

Influence of bath temperatures on physical and electrical properties of potentiostatically deposited Cu2O thin films for heterojunction solar cell applications

In the present work, the influence of bath temperatures on structural, morphological, vibrational, optical, electrical and photo response properties of the electrochemically deposited cuprous oxide (Cu2O) thin films on fluorine doped tin oxide substrate is extensively investigated with the help of X-ray diffraction (XRD), scanning electron microscopy (SEM), Micro Raman spectroscopy, photo luminescence (PL) spectroscopy, UV–visible spectroscopy, LCR measurement, Keithley 4200 semiconductor characterization system respectively. XRD patterns reveal that the deposited Cu2O films have cubic structure grown along the preferential (111) orientation and the film deposited at 40 °C shows better crystalline nature when compared at 55 and 70 °C. The micro structural properties of films such as crystallite size (D), dislocation density (δ), micro strain (e) and stacking fault probability (α) were calculated and discussed in detail. SEM displays a well-defined three side pyramid shaped morphology for the film deposited at 40 °C. Micro Raman and PL spectra reveal the film deposited at 40 °C by being better crystalline at a higher acceptor concentration. UV–Visible study shows that the optical energy band gap increases from 2.05 to 2.17 eV with an increase in bath temperature from 40 to 70 °C. The frequency-temperature dependence of impedance analysis shows a higher electrical conductivity for a film deposited at 40 °C compared to other bath temperatures. I-V measurement illustrates a good photoconductivity response for Cu2O thin film deposited at 40 °C compared to films deposited at 55 and 70 °C.

Voltage-Induced Charge Redistribution in Cu(In,Ga)Se2 Devices Studied With High-Speed Capacitance–Voltage Profiling

Devices made from Cu(In,Ga)Se2 (CIGS) solar cell material have been evaluated with high-speed capacitance–voltage profiling after stepwise voltage changes. The changes primarily affect near-interface charge at deep acceptors within the CIGS absorber layer and generate temperature-dependent capacitance changes observed in deep-level transient spectroscopy measurements. SCAPS device modeling indicates that the deep acceptor concentration is up to the two orders of magnitude higher than the shallow doping level. High deep acceptor concentrations are found in all materials studied here. The large deep defect levels are high enough to limit minority carrier lifetime and cell efficiency.

Pb-doped Cu3Se2 nanosheets: Electrochemical synthesis, structural features and optoelectronic properties

Thin films of nanostructured un- and lead (Pb)-doped copper selenide (Cu3Se2) with various Pb concentrations were grown on fluorine-doped tin oxide (FTO) glass substrates through an electrochemical deposition method. The structural, optical, electrical and photovoltaic properties of the deposited films were studied using different techniques. The X-ray diffraction (XRD) patterns showed polycrystalline tetragonal structures for the Cu3Se2 nanostructures and the field emission scanning electron microscopy (FESEM) images exhibited that all deposited Cu3Se2 films contain nanosheets. The nanosheets of the Pb-doped samples were observed to be bent and fractured at edges. Furthermore, photoluminescence (PL) analysis of Cu3Se2 unraveled three emission bands in the ultraviolet, green and infrared regions and outlined a shift towards lower wavelengths (blue shift) for the near band edge (NBE) of the Pb-doped samples, compared with the un-doped sample. Also, the absorption spectra of the samples were analyzed to determine the optical energy band gap of the samples, which resulted in the value of 1.65 eV for the un-doped sample and demonstrated an increase in the optical energy band gap of Cu3Se2 upon adding Pb dopant and increasing its concentration. Finally, evaluation of the films as the absorber layer of solar cells indicated that there is a minimum amount of strain in the sample with the highest acceptor concentration, which affects its solar cell efficiency, positively.

Nonradiative energy transfer and ion-ion interactions in terbium-praseodymium coactivated borate glass

A study of energy transfer between Tb3+ and Pr3+ in borate glass is being presented. From our measurement of fluorescence emission and decay times of donor (Tb3+), in the presence of different concentrations of acceptor (Pr3+), the energy transfer probability (Pda) and transfer efficiency (ɳT) have been calculated. Analyzing the data it is observed that the non-radiative energy transfer in our borate glass system occurs by dipole-dipole interactions, contrary to the observations made by Nakazawa and Shionoya (dipole-quadrupole interaction) in phosphate glass. A linear dependence of Pda versus C at low acceptor concentration suggests the migration of excitation energy among donor ions before the energy is finally transferred to the acceptor ion. At high acceptor concentrations a plot of Pdavs (C0 + C)2; where C0 is donor concentration and C is the acceptor concentration, presents a linear dependence suggesting thereby that one donor interacts with two neighbouring acceptors consistent with Fong-Diestler mechanisms of dipole-dipole energy transfer interactions.

Demonstration of 13-kV Class Junction Barrier Schottky Diodes in 4H-SiC with Three-Zone Junction Termination Extension

The static and dynamic characteristics of 13-kV class 4H-SiC junction barrier Schottky (JBS) diodes with a three-zone junction termination extension (JTE) are presented. Using an anisotropy breakdown model, technology computer-aided design simulation of devices with a three-zone JTE agrees well with the obtained experimental results, correctly predicting a sharp drop in blocking voltage at high JTE acceptor concentrations. The forward voltage of the JBS diode at 75°C and a forward current of 500 mA is reduced to approximately one-ninth by that of 13 series-connected 1000-V Si PiN diodes. This suggests that conduction losses of traditional high-voltage circuits which conventionally use series-connected devices can be drastically reduced by replacing the series-connected devices with a single 13-kV class SiC JBS diode. Moreover, the reverse recovery current waveform of the 13-kV class SiC JBS diode shows that these diodes have lower reverse recovery losses than a 13-kV SiC PiN diode.

On the electrochemical synthesis and characterization of p-Cu2O/n-ZnO heterojunction

A p-Cu2O/n-ZnO heterojunction was grown directly on fluorine-doped tin oxide (FTO) substrate by two-step electrodeposition in aqueous solution. The electrical characteristics of the p-Cu2O/FTO and n-ZnO/FTO were studied using the Mott-Schottky (M-S) analysis in the electrolyte solution. High donor and acceptor concentrations were obtained for ZnO and Cu2O layers, respectively. The p-Cu2O/n-ZnO heterojunction show long electron lifetime and high electron–hole separation efficiency according to the electrochemical impedance spectroscopy (EIS) measurements and photocurrent response. The morphological, structural, optical, and electrical characteristics of p-Cu2O/n-ZnO heterojunction were investigated by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), UV–Vis and photoluminescence (PL) analysis. The FE-SEM cross-section images confirm the formation of well-defined cubic Cu2O grains on continuous and flat surface of ZnO layer. XRD result points to high crystallinity of (111)-oriented p-Cu2O layer on (101)-oriented n-ZnO layer. The optical band gap energies of n-ZnO and p-Cu2O thin film are 3.3 and 2.3 eV, respectively. The current–voltage (I–V) characteristics of Au/p-Cu2O/n-ZnO/FTO heterojunction shows well-defined rectifying behavior with turn on voltage of 0.5 V in dark and high photoresponse under illumination.