Low Ideality Factor Research Articles

High-current, high-voltage AlN Schottky barrier diodes

AlN Schottky barrier diodes with low ideality factor (<1.2), low differential ON-resistance (<0.6 mΩ cm2), high current density (>5 kA cm−2), and high breakdown voltage (680 V) are reported. The device structure consisted of a two-layer, quasi-vertical design with a lightly doped AlN drift layer and a highly doped Al0.75Ga0.25N ohmic contact layer grown on AlN substrates. A combination of simulation, current–voltage measurements, and impedance spectroscopy analysis revealed that the AlN/AlGaN interface introduces a parasitic electron barrier due to the conduction band offset between the two materials. This barrier was found to limit the forward current in fabricated diodes. Further, we show that introducing a compositionally-graded layer between the AlN and the AlGaN reduces the interfacial barrier and increases the forward current density of fabricated diodes by a factor of 104.

The influence of oxygen partial pressure on the properties of sputtered vertical NiO/β-Ga2O3 heterojunction diodes

In this work we present studies on the influence of oxygen partial pressure on the properties of sputtered vertical NiO/β-Ga2O3 heterojunction diodes. Obtained results shows substantial effect of oxygen partial pressure on the electrical properties of NiO/β-Ga2O3 heterojunction diodes. The diodes with NiO layers deposited in pure Ar shows Schottky-like I-V characteristics with low ideality factor of 1.05 and barrier height of 1.27 eV as well as low turn-on voltage close to 1V. On the other hand, diodes with NiO layer deposited in oxygen containing atmosphere shows typical p-n diode characteristics. The best electrical characteristics i.e. low on-state resistance of 2.85 mΩcm2, lack of defects and low ideality factor down to 1.07 at RT along with high breakdown voltage close to 900V without any junction termination, were obtained for diodes with NiO layers deposited at 50 % oxygen content. We have demonstrated that by optimization of oxygen partial pressure, the properties of NiO/β-Ga2O3 heterojunction diodes can be tuned and excellent electrical performance in terms of low-on state resistance, high breakdown voltage, low-leakage current and low ideality factor, can be obtained.

Microstructure Evolution and Electrical Behaviors for High-Performance Cu2O/Zr-Doped β-Ga2O3 Heterojunction Diodes.

Beta-gallium oxide (β-Ga2O3) is emerging as a promising ultrawide band gap (UWBG) semiconductor, which is vital for high-power, high-frequency electronics and deep-UV optoelectronics. It is especially significant for flexible wearable electronics, enabling the fabrication of high-performance Ga2O3-based devices at low temperatures. However, the limited crystallinity and pronounced structural defects arising from the low-temperature deposition of Ga2O3 films significantly restrict the heterojunction interface quality and the relevant electrical performance of Ga2O3-based devices. In this work, cuprous oxide (Cu2O)/Zr-doped β-Ga2O3 heterojunction diodes are fabricated by magnetron sputtering without intentional substrate heating, followed by an investigation into their microstructure and electrical behaviors. Zr doping can markedly enhance the Ga2O3 crystallinity at low substrate temperatures, transforming the amorphous structure of pristine Ga2O3 films into the crystallized β phase. Moreover, crystalline β-Ga2O3 facilitates the epitaxial growth of the Cu2O phase, suppressing the formation of detrimental secondary phase CuO at the heterojunction interface. Benefiting from the high-quality heterojunction interface, the Cu2O/Zr-doped β-Ga2O3 heterojunction diode exhibits a near-ideal electrical behavior with a low ideality factor of 1.6. The consistent electrical parameters extracted from current-voltage (J-V) and capacitance-voltage (C-V) measurements also confirm the high quality of β-Ga2O3. This work highlights the potential for the low-temperature production of high-quality β-Ga2O3-based heterojunction devices through Zr doping.

Light induced degradation of CIGS solar cells

Considering warranted lifetimes of PV modules of typically 20-30 years, the performance stability of PV modules is one of the most crucial factors regarding power generation and yield. Long term outdoor performance studies depict realistic operation conditions best, but the correlated nature of e.g. irradiance and temperature impedes the physical interpretation. The possibility to control and tune the conditions in laboratory experiments enables to decompose effects, that are typically overlayed in outdoor experiments. This way, laboratory are crucial to interpret the results obtained in outdoor degradation studies. One driving force of degradation of CIGS modules is light exposure. In literature the focus of light induced degradation (LID) of CIGS modules and solar cells is on metastable changes analyzed on time scales ranging from minutes to hours. In this work we expose industrially produced encapsulated CIGS solar cells for more than 1000 h to light with varied intensity under varied temperature conditions. Such, we aim to study temperature and light intensity dependencies of the observed performance changes. Furthermore, we study the influence of applied bias by comparing LID at short and open circuit. We demonstrate that LID under short circuit conditions leads to VOC degradation, while being temperature assisted and not dependent on the irradiance intensity. CIGS solar cells kept at open circuit conditions appear to be stable under illumination. Exploiting the one diode model, we further connect the observed temperature assisted performance loss to enhanced recombination with lower ideality factor, in comparison to the dominant recombination process before degradation.

Reduced graphene oxide decorated CuO@NiO nanocomposite and their improved photosensitive activity for photodetection applications

In our proposed work, pure rGO and CuO@NiO/rGO (CNR) nanocomposites (NCs) with different ratios of CuO@NiO:rGO (90:10, 75:25 and 50:50) were synthesized and explored by XRD, SEM with EDX, TEM, XPS, UV–visible, PL and utilized to measure the current – voltage characteristics under dark and illumination conditions. TEM analysis indicates ultra-thin nanosheets of rGO with lengths of several tens of micrometer and CuO@NiO particle sizes is ∼50 nm. XPS analysis showed the presence of element and chemical states for Cu, Ni, O, and C in CNR-(50:50) sample. The energy gap (Eg) of pure rGO is 3.99eV whereas the CNR for 90:10, 75:25 and 50:50 NCs energy gap (Eg) values are viz., 1.43eV, 1.41eV and 1.39eV. The diode characteristic of CNR-(50:50)/n-Si exhibit lower ideality factor (n = 1.96), higher barrier height (ΦB = 0.80eV) under illumination condition. The CNR-(50:50)/n-Si photodiode exhibits higher photosensitivity (PS), responsivity (R), External Quantum Efficiency (EQE) and detectivity (D*) values of 956.45 %, 656.29 mA/W, 367.6/1 % and 5.72 × 1012 (Jones) respectively.

Influence of material properties of liquid absorption filters for concentrated photovoltaic/thermal hybrid systems

A concentrated photovoltaic/thermal system with a liquid filter is an effective technique to utilize the whole solar spectrum for power production. However, fundamental issues still need further investigation, including the structure of flow design and absorptive fluid selection principles. This paper presents a comparative study of optimized configurations of fluid flow channels in a concentrated photovoltaic/thermal system. MATLAB was used to study the influence of fluid thermal properties and transmittance on the system performance. The results showed that increasing the ideality factor from 0.5 to 1 can improve the overall exergy efficiencies of the coupled and decoupled concentrated photovoltaic/thermal system by 2.2 % and 2.4 %, respectively. Moreover, it was found that the coupled concentrated photovoltaic/thermal is more suitable for electrical production when the heat capacity exceeds 2500 J/kgK. The coupled system’s outlet temperature is boosted to 20˚C when the ideality factor is decreased by 20 % but requires significantly lower specific heat capacities. Overall energy efficiency tends to be higher at high heat capacity and low ideality factor values, while exergy efficiency tends to be higher at high heat capacity and high ideality factor values.

Study on structural, optical, and electrical properties of yttrium doped molybdenum oxide thin film and its MIS diode performance

In this study, Orthorhombic pure MoO3 and various weight percentages of Y-doped MoO3 nanostructure arrays were successfully deposited using the simple jet nebulizer spray pyrolysis process at an ideal substrate temperature of 500 °C. In order to create metal-insulator-semiconductor-based Schottky barrier diodes, Y-doped MoO3 nanostructure arrays were employed as an insulating layer. The influence of Y-doped MoO3 concentration during the deposition process was carefully analyzed in relation to the structural, morphological, optical, and electrical characteristics of Y-doped MoO3 nanostructure array films. The produced films' crystalline nature with an orthorhombic phase was shown by the XRD pattern. An FE-SEM was used to analyse the solidly linked plate-like structure of Y-doped MoO3 at higher concentrations of 6 wt%. The EDAX spectrum was used to confirm the stoichiometric relationship between the elements O, Mo, and Y. The band gap values of the Y-doped MoO3 were determined using UV–Vis spectroscopy to range from 3.3 to 3.18 eV with doped concentrations. The film made with 6 wt% Y doped MoO3 showed a sharp improvement in electrical conductivity according to a DC electrical analysis. Notably, MIS diode made with 6 wt% Y-doped MoO3 in particular showed a low ideality factor (n = 2.63), strong photosensitivity (PS = 17,509.62%), responsivity of 738 mA/W, and a maximum QE of 97.49% under illumination (130 mW/cm2). Additionally, a 6 wt percent Y-based diode obtained a greater detectivity of D* = 7.16 1009 jones in a dark environment condition.

60‐4: Minimal Efficiency Degradation and Elevated Radiometric Power Density of Ultraviolet‐A Micro‐LED with Homoepitaxial Structure

As display technology continues to advance, UVA micro‐LEDs are becoming increasingly important in a variety of display and beyond‐display applications. In this study, we investigate the optoelectronic characteristics of UVA micro‐LEDs based on a homogeneously epitaxial structure on freestanding gallium nitride (GaN) substrates. The device exhibits a central wavelength of 390 nm, positioned at the overlap of UVA and visible light spectra. It demonstrates an impressively low ideality factor of 1.49 at 2.86 V and a series resistance of 9.88 O beyond 3 V. Optically, our device shows virtually no wavelength shift across a wide current density range of 0.1‐1000 A/cm2, indicating exceptional optical stability and color accuracy. The emitted light is typical purple, reaching an expansive color gamut of 115.3% of Rec.2020. Furthermore, the GaN‐on‐GaN structure, with its superior crystal structure and heat dissipation properties, results in a very low droop ratio in EQE. This ensures sustained highpower output at high current densities, showcasing great potential in applications such as 3D printing, maskless photolithography, and fluorescence tagging.

Role of interfacial layer as PANI–silicene in Si-based photodiodes

Silicene is a 2D monoatomic sheet of silicon and can be used for various applications such as degradation, therapy, and biosafety. Polyaniline (PANI) is a conducting polymer employed for electronic devices. In this study, we synthesized PANI–silicene composites and operated as an external interfacial layer between Al and different type substrates of p-Si and n-Si to compare Schottky-type photodiodes of PANI–silicene/n-Si and PANI–silicene/p-Si. The silicene structures were investigated using X-ray diffractometry (XRD) and scanning electron microscopy (SEM) techniques. Also, the light power intensity dependent of PANI–silicene/n-Si and PANI–silicene/p-Si photodiodes carried out in the range 0–100 mW/cm2 and I–t measurements utilized to determine the response time of the photodiodes. Basic parameters of devices such as ideality factors barrier, height, and series resistance were obtained by Norde and Cheung methods and thermionic emission (TE) theory from I–V graphs. While the PANI–silicene/n-Si exhibited high ideality factor values of 5.49, the PANI–silicene/p-Si photodiodes showed a low ideality factor of 1.48. The photodiode parameters such as detectivity and responsivity were calculated as 6.40 × 109 Jones and 38.9 mA/W for n-Si substrate and 78.2 mA/W and 8.81 × 109 Jones for p-Si substrate. The case of basic electrical properties for PANI–silicene composite interlayer-based photodiodes was analyzed in detail.

Separation of wafer bonding interface from heterogenous mismatched interface achieved high quality bonded Ge-Si heterojunction

In the realm of optoelectronic integration, silicon-based Ge bonding has attracted great attention due to its advantages in short-wave infrared response and low cost. However, owing to the inherent lattice mismatch and thermal mismatch between Ge and Si, the bonded Ge-Si heterogenous interfaces encountered problems of thermal instability and high interface states. Herein, an approach of separating the bonding interface from the heterogenous interface is proposed through inserting a Ge epitaxial layer (GeEL) between the Si substrate and Ge film. This separation modifies the bonding interface to a homogenous one, alleviating the massive mismatch stress and achieving film relaxation, enhancing bonding stability in all aspects. Moreover, during 850 °C annealing, GeEL is doped via diffusion hence realizes electric filed modulation, inhibiting the carrier recombination leakage current and trap assisted tunneling in this defect-rich layer. A Ge-Si heterogenous PIN diode prepared by this bonding method has achieved a remarkable low dark current density (1.33 mA/cm2), a low ideality factor (1.11), and a high on–off ratio (106), confirming the outstanding quality of the bonded heterojunction. This work provides great prospects for higher performance, larger scale and multi-functional Si-based heterogenous material device applications.

Studies of NiO/Ag/NiO transparent conducting electrodes on NiO and ZnO Schottky diodes.

A nickel oxide (NiO)/silver (Ag)/NiO (NAN) transparent conducting electrode (TCE) was deposited on NiO and zinc oxide (ZnO) to fabricate Schottky diodes (SDs). The physical and electrical properties of NAN/NiO and NAN/ZnO SDs were studied. In addition, conventional Au/ZnO SDs were fabricated for comparison. The prepared NAN TCE was of n-type, with more than 40% transmittance and a low sheet resistance of 6.5 Ω sq.-1, indicating that NAN is an exceptional TCE. Secondary ion mass spectrometry revealed that Ag atoms diffused into NiO and ZnO in the NAN/NiO and NAN/ZnO SDs, respectively. Owing to the large number of defects on the ZnO surface, the current-voltage (I-V) characteristics of the Au/ZnO SDs followed a linear curve. However, the reduced number of defects and a large barrier height at the NAN/ZnO interface led to a rectifying I-V curve in NAN/ZnO SDs. In contrast, a near homojunction at the NAN/NiO interface caused a linear I-V curve and a large leakage current in NAN/NiO SDs. These issues resulted in a lower ideality factor (5.32) in NAN/ZnO SDs than that in NAN/NiO SDs (15.14). The NAN/ZnO SDs exhibited a higher barrier height (0.91 eV) than the NAN/NiO SDs (0.55 eV). The mechanism of carrier transport was investigated using a ln(I) versus ln(V) plot. The NAN/NiO SDs only exhibited one region of ohmic conduction. However, two distinct regions were observed in the NAN/ZnO SDs. For V ≤ 0.7 V, the space-charge-limited current dominated; however, the diffusion-recombination model controlled carrier transport at V ≥ 0.7 V. Band diagrams were proposed to elucidate the carrier transport mechanism in NAN/NiO and NAN/ZnO SDs.

Improving vertical GaN p–n diode performance with room temperature defect mitigation

Defect mitigation of electronic devices is conventionally achieved using thermal annealing. To mobilize the defects, very high temperatures are necessary. Since thermal diffusion is random in nature, the process may take a prolonged period of time. In contrast, we demonstrate a room temperature annealing technique that takes only a few seconds. The fundamental mechanism is defect mobilization by atomic scale mechanical force originating from very high current density but low duty cycle electrical pulses. The high-energy electrons lose their momentum upon collision with the defects, yet the low duty cycle suppresses any heat accumulation to keep the temperature ambient. For a 7 × 105 A cm−2 pulsed current, we report an approximately 26% reduction in specific on-resistance, a 50% increase of the rectification ratio with a lower ideality factor, and reverse leakage current for as-fabricated vertical geometry GaN p–n diodes. We characterize the microscopic defect density of the devices before and after the room temperature processing to explain the improvement in the electrical characteristics. Raman analysis reveals an improvement in the crystallinity of the GaN layer and an approximately 40% relaxation of any post-fabrication residual strain compared to the as-received sample. Cross-sectional transmission electron microscopy (TEM) images and geometric phase analysis results of high-resolution TEM images further confirm the effectiveness of the proposed room temperature annealing technique to mitigate defects in the device. No detrimental effect, such as diffusion and/or segregation of elements, is observed as a result of applying a high-density pulsed current, as confirmed by energy dispersive x-ray spectroscopy mapping.

Dependence of diode behaviour and photoresponse of Ga-doped ZnO (GZO)/p-Si junction on the carrier concentration of GZO layer

Ga-doped ZnO (GZO)/p-Si junctions were fabricated by reactive co-sputtering of Zn-GaAs target in Ar–O2 atmosphere. Highly degenerate GZO (carrier concentration ∼1021 cm−3) deposited at 4 % O2 forms non-rectifying contact with p-Si. GZO/p-Si diodes fabricated with moderately doped GZO layers deposited at 5 % O2, having carrier concentration ∼1019 cm−3 display low turn-on voltage (≲ 0.5 V) and ideality factor ≈ 2. Measurement of barrier height by temperature dependent I–V and built-in potential by C–V reveal respective values of (0.74 ± 0.07 eV) and (0.44 ± 0.04 eV), suggesting formation of Schottky type diodes. These diodes display nearly linear I–V characteristics under UV illumination, yielding photoresponsivity ∼1 A/W at ± 1 V. In contrast, GZO/p-Si diodes fabricated with lightly doped (non-degenerate) GZO layers deposited at 6–8 % O2, having carrier concentration ∼1018 cm−3, show higher turn-on voltages (4.5–6.5 V) and ideality factors of 2.5–2.7. I–V and C–V measurements reveal nearly equal values of barrier height and built-in potential, indicating formation of n-p heterojunctions, with near-elimination of conduction band discontinuity. Under UV illumination, I–V characteristics of these GZO/p-Si diodes display non-linear behaviour in forward bias and yield photoresponsivity of ∼0.1 A/W at ±1 V.

Identification and classification of Eremogone species using DNA based Schottky diodes

The revelation of DNA's remarkable conducting characteristics provided a significant boost for the development of DNA-based electronics. These distinguishing characteristics can be used to identify or detect DNA. In this study, it was basically aimed to investigate the possibility of using Schottky barrier diodes in which semiconductor DNA is used as the interface from three endemic Eremogone species distributed in Turkey. We collected Eremogone ali-gulii, Eremogone armeniaca, and Eremogone scariosa endemic species and extracted the DNA via the QIAGEN commercial DNA isolation kit procedure. The DNA samples were deposited by drop casting on the thin film indium tin oxide substrate. Electrical characterization of DNA interlayered heterojunctions was investigated via a solar simulator. Electronic parameters such as ideality factor, barrier height, and series resistance were calculated from I to V characteristics. Electrical properties of DNA samples were investigated and compared to Colchicum triphyllum’s DNA which is completely from another genus. The results show that morphologically similar species have similar electrical properties. When compared to Colchicum triphyllum-DNA based device, genus Eremogone-DNA based devices have a lower ideality factor, barrier height, and series resistance. Via this technique, DNA samples can be identified, detected, and classified.

Demonstration of near-ideal Schottky contacts to Si-doped AlN

Near-ideal behavior in Schottky contacts to Si-doped AlN was observed as evidenced by a low ideality factor of 1.5 at room temperature. A temperature-independent Schottky barrier height of 1.9 eV was extracted from temperature-dependent I–V measurements. An activation energy of ∼300 meV was observed in the series resistance, which corresponded to the ionization energy of the deep Si donor state. Both Ohmic and Schottky contacts were stable up to 650 °C, with around four orders of magnitude rectification at this elevated temperature. These results demonstrate the potential of AlN as a platform for power devices capable of operating in extreme environments.

Electrical properties of CuO/ZnO heterojunctions prepared by spray pyrolysis

In the present work we investigate the influence of deposition sequences on the two layers forming a CuO/Zinc oxide (ZnO) heterojunction. Both layers are prepared using the simple and cost-effective technique of spray pyrolysis. The advantage of this technique is the ability to deposit both layers successively without interruption. For this purpose, four devices are prepared by successfully changing the deposition order of ZnO and CuO layers, and after a delay for the cooling of the first deposited layer. The I–V characteristics of the realized devices reveal that the deposition order plays a crucial role in the device’s performance. We inferred that the deposition of ZnO as the first layer followed by the immediate CuO leads to a device with superior quality, i.e., low ideality factor, low reverse current, and high rectifying ratio. The SEM image and EDX analysis at the interfaces revealed the diffusion of Zn in the CuO layer, while no diffusion of Cu in the ZnO layer was observed. Estimating the density of the interface states from the conductance vs. frequency measurements (G–f) indicates that the direct deposition of CuO on ZnO leads to a lower interface density of states.

Reducing specific contact resistivity for n-type germanium using laser activation process and nano-island formation

This study presents a laser activation process (LAP) for germanium (Ge) to improve the electrical performance of n-type Ge devices. The LAP highly activated the dopant and created a shallow junction in Ge. We also investigated a triple contact of titanium (Ti)/nickel (Ni) nano-island/Ge to reduce contact resistivity and enhance the tunneling current. The results showed that the LAP with a fluence of 140 mJ/cm2 effectively activated the dopant, resulting in a high forward current density and a low ideality factor of the n+-p junction diode. The triple contact of Ti/Ni nano-island/Ge showed the lowest specific contact resistivity, indicating an increase in the tunneling current. The Ni nano-island contact showed the best overall electrical performance, attributed to the boosted electric field and the lower density of states at the interface. The results show that combining multiple approaches, including the optimized laser activation process and triple contact formation, can significantly reduce the contact resistance on n-type Ge, providing a promising approach for improving performance.

Investigation of deep defects and their effects on the properties of NiO/β-Ga2O3 heterojuncion diodes

In this study, the effect of rapid thermal annealing (RTA) on the electrical and optical properties of NiO/ β-Ga2O3 heterojunction diodes was investigated using capacitance-voltage, current-voltage, Deep Level Transient Spectroscopy (DLTS), Laplace DLTS, photoluminescence and micro-Raman spectroscopy techniques, and SILVACO-TCAD numerical simulator. The NiO is designed to be lowly-doped, allowing for the NiO full depletion at zero bias and the study of properties of β-Ga2O3 and its interface with NiO. Micro-Raman results revealed good agreement with the theoretical and experimental results reported in the literature. The photoluminescence intensity of the sample after RTA is five times higher than the fresh sample due to a rise in the density of gallium and oxygen vacancies (VGa + VO) in the annealed β-Ga2O3 samples. The current-voltage characteristics showed that annealed devices exhibited a lower ideality factor at room temperature and higher barrier height compared with fresh samples. The DLTS measurements demonstrated that the number of electrically active traps were different for the two samples. In particular, three and one electron traps were detected in fresh samples and annealed samples, respectively. SILVACO-TCAD was used to understand the distribution of the detected electron E2 trap (Ec-0.15 eV) in the fresh sample and the dominant transport mechanisms. A fairly good agreement between simulation and measurements was achieved considering a surface NiO acceptor density of about 1 × 1019 cm−3 and E2 trap depth into the surface of β-Ga2O3 layer of about 0.220 µm and the effect of the most observed Ec-0.75 eV trap level in β-Ga2O3. These results unveil comprehensive physics in NiO/β-Ga2O3heterojunction and suggest that RTA is an essential process for realizing high-performance NiO/β-Ga2O3devices.

Doping Density Extraction of Plasma Treated Metal Oxide Thin Film Diodes by Capacitance–Voltage Analysis

AbstractHigh quality thin film p‐n junction diodes with high rectification ratios and low ideality factors have been fabricated from metal oxides, such as amorphous oxide semiconductors (AOSs), and characterized. Plasma treatment of interfaces has been demonstrated to improve devices made from AOSs, using current–voltage (I–V) measurements. However, capacitance–voltage (C–V) measurements of the devices have been scarcely reported in the literature. Therefore, the focus of this work is characterization of cuprous oxide (Cu2O)/amorphous zinc‐tin oxide (a‐ZTO) thin film heterojunction diodes using C–V analysis. Performance differences of plasma‐treated and untreated diodes that are difficult to observe in I–V analysis are more prominent in C–V analysis. Moreover, C–V analysis allows extraction of charge density profiles, which is a measure of the defect state density that led to intrinsic doping. The variation of doping densities of the untreated diode across the full range of applied reverse bias is shown to be up to 2 orders of magnitude, while those of the treated diodes are within a factor of 10 only. Junction charge profiles, interfacial charge depletion, and accumulation that are key features of rectifying diodes are shown to be clearly distinct between untreated, nitrogen‐treated, and oxygen‐treated diodes, thus explaining why oxygen‐treated diodes are superior.

The possibility of gallium oxide (β-Ga2O3) heterojunction bipolar transistors

Bipolar junction transistors have not been viable with β-Ga2O3 due to its poor hole mobility and unavailability of shallow acceptors. Many p-type oxides form high-quality heterojunction diodes (low ideality factor and high breakdown voltage) with β-Ga2O3. We propose using these heterojunctions to make a β-Ga2O3 heterojunction bipolar transistor (HBT). Cu2O/β-Ga2O3 heterojunction is especially promising because of the relatively high electron diffusion length (∼μ m) in Cu2O, a low electron injection barrier at the Cu2O-Ga2O3 interface, and breakdown voltages of >1000 V. Using Silvaco TCAD, we simulate a β-Ga2O3 heterojunction bipolar transistor with a Cu2O base and estimate the power figure of merit (PFOM). We find that the low bandgap of Cu2O severely limits the performance of these HBTs. Reports of Cu2O-Ga2O3 diodes with extremely high breakdown voltage are probably due to heavily doped Cu2O or interface defects, but these effects do not translate to the HBT. For HBTs with PFOM better than the state-of-the-art β-Ga2O3 unipolar transistors, we need alternative p-type oxides with a bandgap E g > 3.4 eV and electron diffusion length >0.4 μ m. We discuss the possible candidates. Using an empirical model for the critical avalanche breakdown field, we estimate the maximum PFOM for possible β-Ga2O3 HBTs.