Polyimide-passivated pn diodes

As the performance of GaN- and SiC-based power devices becomes limited by fundamental material properties, semiconductors with larger bandgaps are appealing due to their superior material properties. Most notable is that the critical electrical field scales as the bandgap to the 2.0-2.5 power. Thus, diodes employing wide bandgap semiconductors are expected to operate at higher breakdown voltages with thinner and more heavily-doped drift regions, leading to lower resistive losses. AlGaN alloys with their much larger bandgap compared to SiC and GaN are thus appealing for high voltage pn diodes and transistors. Additionally, the formation of AlGaN-based heterojunctions and the utilization of polarization fields offer design options not possible for devices based on materials such as SiC and diamond. Here we report on the growth and performance of pn diodes fabricated from Al0.30Ga0.70N (Eg=4.1eV) and Al0.74Ga0.26N (Eg=5.3eV) alloys, illustrating the potential for AlGaN alloys as a viable material for next-generation power diodes. Quasi-vertical pn diodes consisting of Al0.30Ga0.70N epilayers were grown by metalorganic vapor phase epitaxy on 1.3 mm thick sapphire substrates. The added stiffness of such thick sapphire substrates (3x thicker than typical sapphire) reduces wafer bow and eliminates cracking in epitaxial structures up to 19 μm thick. Thick epitaxial structures are needed to achieve the > 4 microns thick drift layers necessary for multi-kilovolt breakdown voltages. A series of pn diode structures were grown where the thickness of the lightly doped drift layer (No = 2-5x1016 cm-3) was varied from 4.3 to 11 μm. All structures were completed with a 0.35 μm thick Mg-doped Al0.30Ga0.70N p-layer followed by a compositional grade to a p-GaN contact layer. Diodes employed a junction edge termination structure around the p-contact to reduce the peak electric field at the contact metal to avoid premature breakdown. Breakdown voltages from 1600 to 3000V were achieved in reverse bias and a forward turn-on voltage of 6 to 8 volts was recorded. To our knowledge, this is the first vertical AlGaN-based pn diode exhibiting a breakdown voltage in excess of 1 kilovolt. The differential specific on-resistance was higher than expected based on consideration of the drift region only (typically 16-20 mΩ-cm2), which is tentatively attributed to the resistance due to lateral current spreading in these front-contacted, quasi-vertical diodes. An effective critical electric field of 5.9 MV/cm was determined from the reverse current-voltage characteristics based on a punch-through, as dictated by the doping and thickness of the drift region. We have also investigated quasi-vertical pn diodes consisting of Al0.74Ga0.26N epilayers to exploit the expected higher critical electric field in higher aluminum mole fraction alloys. These diodes consisted of 4.5 μm thick AlN epilayers grown on sapphire followed by a heavily doped n-type contact layer. Next a lightly doped (No = 2-4x1016 cm-3) 5 or 8 μm thick drift layer was grown. The combination of a thick AlN buffer and Al0.74Ga0.26N layers resulted in x-ray diffraction linewidths of 164-197 (237–284) arc seconds for the (0002) and (10-12) reflections for the drift layer, respectively. By optimizing the growth conditions used for the drift layer, the density of electron compensating defects can be reduced to ~ 1x1016 cm-3 — a level reported for GaN pn diodes. Unlike GaN diodes where drift layer doping at mid to low 1015 cm-3 is necessary for breakdown voltages of several kilovolts, the free electron concentration in these Al0.74Ga0.26N pn diodes is significantly higher than the level of compensation, making doping much easier to control and illustrating the benefit of higher critical electric field. The drift layer was followed by p-type AlGaN and finally a compositional grade to a p-GaN contact layer. It is the p-AlGaN layer that is a significant challenge in Al-rich pn diodes. Unlike pn diodes based on Al0.30Ga0.70N epilayers, simple homojunction pn diodes are not practical in Al-rich AlGaN alloys due to the low hole concentration owing to the very deep (Ea > 400 meV) acceptor level. Consequently, other approaches must be considered for hole transport to the pn junction. We will report on the current-voltage characteristics of pn heterojunction diodes where a Mg-doped p-type Al0.30Ga0.70N layer is grown on the n-type Al0.74Ga0.26N drift layer. Additionally, the current-voltage characteristics of pn diodes where holes are generated in the p-region by field ionization of Mg acceptors will also be presented. Finally, practical pn diodes require specific on-resistance lower than what is inherent for front-contacted quasi-vertical device architectures grown on insulating substrates. We will report an approach that has realized vertically conducting AlGaN pn diodes employing AlGaN overgrowth on conducting GaN substrates.

Devices were fabricated in MBE (molecular-beam epitaxy)-grown wafers with a ten period doping superlattice consisting of 300-AA layers with n=p=3*10/sup 18/ cm/sup -3/, using sequential patterned sulfur and zinc diffusions. The typical contact spacing was 5 mu m, and the devices were generally 400 mu m long. Excellent I-V characteristics were achieved with reverse breakdown voltages in excess of 9.5 V, indicating that the selective contacts were nearly optimum. CW outputs of 500 mu W at 50-mA drive current have been observed from the surface of the devices at room temperature. Measurements of the current-voltage characteristics and electroluminescence spectra have been performed from 3 to 300 K. The LED output spectrum tuned at a rate of about 700 meV/V of applied bias at 120 K. Good correlation was observed between the forward characteristics of the diodes and the tuning of the electroluminescence. The tunneling component of the diode current has been identified and remains significant to temperatures of approximately=140 K. As the tunneling component is reduced, the tunable luminescence is quenched due to the competition from thermally injected carriers recombining across the bandgap.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

lnAs diode detectors are good for -3 pm wavelength detection and promising to operate at high temperature (T). In order to decrease the dark current at high T, we have studied the I-V characteristics of the PIN (S1066) and PN (SI 135) diodes, and concluded the dominant current mechanics at various T. The two diodes are grown on the lnAs N-type substrates. The doping densities of the PN diode are 3x10 and 6.7~10'~ cm-' for P and N types res ctively, and the thickness of the intrinsic layer is 0.14 pm. Those of the PN diode are IxlO'* cm and IxlO'cm. The mesa shape of the diodes is a circle wlth a radius of I50 pm. The analysis of [he experimental results is based on the model of a tunnel diode[ I] The solid and own symbols in Fig. I represent the results of the PIN and PN diodes respectively. At low T, the reverse current is almost conslant and increases dramatically at around 300K. The dashed lines are the fitting diffsuion current at 300K. Re derived energy bandgap by the fitting is 0 38 eV, and consistent with that of InAs. In addition, the E diffusion currenl ofthe PIN diode is about 3.3 times higher than that of the 5'. PN diode This agrees well with the ratio of the P-type doping densities of the two diodes under the assumption that the dominant diffusion current is '2 due to the electron diffusion in the P-type material. At low T, the constant 5 10% current is attributed to the Zener current and caused by the elecmn 2 tunncling rrom the P-type valence band to the N-type conduction band. At V = 0.01 volt for the PN diode. due to small Zener current, the generationrecombination current is seen as shown in the doned line ofthe figure.

A PIN light emitting diode (LED) was fabricated from a p-Ge/i-Ge/n-Si heterojunction structure grown by using rapid thermal chemical vapor deposition. The structural properties of the p-Ge/i-Ge/n-Si heterojunction structure were investigated using high-resolution X-ray diffraction. Specifically, recent advances in the dry etching of the p-Ge/i-Ge/n-Si heterojunction structure were used to define PIN LED p-Ge/i-Ge layer mesas. The I-V characteristic of the PIN LED indicate a reasonable reverse saturation current of 96 µA at − 1 V and a high reverse breakdown voltage in excess of − 100 V. The roll-off in the electroluminescence spectrum above a wavelength of 1700 nm is thought to the decreased emission in the p-Ge/i-Ge/n-Si pin LED at room temperature.

The issues of creating powerful power propulsion systems (PPS) based on a thermionic reactor-converter (TRC) and electric rocket propulsion systems (ERPS) are related to the development of compact high-temperature radiation–resistant current conversion systems (CCS) using plasma electric power devices - grid key elements (GKE) and high-voltage plasma thermionic diodes (HVPTD). The main problem of the development of GCE and HVPTD is the determination of their operating voltage (or reverse arc breakdown voltage in the locked state), which together with the current density in the conductive state characterizes the electric power density of the valve and is its main parameter. Within the framework of this work, the authors, based on the study of the locked state, numerically and analytically obtained new dependences for calculating the reverse arc breakdown voltage and determined the limiting values of the electrical power density of the HVPTD.

A systematic investigation of the electrical characteristics of β-Ga2O3 Schottky barrier diodes (SBDs) has been conducted under high-dose 60Co gamma radiation, with total cumulative doses reaching up to 5 Mrad (Si). Initial exposure of the diodes to 1 Mrad resulted in a significant decrease in on-current and an increase in on-resistance compared to the pre-radiation condition, likely due to the generation of radiation-induced deep-level acceptor traps. However, upon exposure to higher gamma radiation doses of 3 and 5 Mrad, a partial recovery of the device performance occurred, attributed to a radiation annealing effect. Capacitance–voltage (C–V) measurements showed a decrease in net carrier concentration in the β-Ga2O3 drift layer, from ∼3.20 × 1016 to ∼3.05 × 1016 cm−3, after 5 Mrad irradiation. Temperature-dependent I–V characteristics showed that 5 Mrad irradiation leads to a reduction in both forward and reverse currents across all investigated temperatures ranging from 25 to 250 °C, accompanied by slight increases in on-resistance, ideality factors, and Schottky barrier heights. Additionally, a slight increase in reverse breakdown voltage was observed post-radiation. Overall, β-Ga2O3 SBDs exhibit high resilience to gamma irradiation, with performance degradation mitigated by radiation-induced self-recovery, highlighting its potential for radiation-hardened electronic applications in extreme environment.

Characteristics of β-SiC/Si heterojunction with a SiGe buffer film

The surface of single-crystal (-201) oriented β-Ga2O3 was etched in BCl3/Ar inductively coupled plasmas under conditions (an excitation frequency of 13.56 MHz, a source power of 400 W, and a dc self-bias of −450 V) that produce removal rates of ∼700 Å min−1. Annealing at 400 and 450 °C was carried out after etching on Ni/Au Schottky diodes formed on the surface either before or after the annealing step. Current–voltage (I–V) measurements were used to extract the Schottky barrier height (Φ), diode ideality factor (n), and reverse breakdown voltage (VRB) for plasma damaged diodes after annealing. Annealing at 450 °C was found to essentially restore the values of Φ, n, and VRB to their reference (unetched) values on samples metallized after etching and annealing. Thermal annealing at either temperature of metallized diodes degraded their reverse breakdown voltage, showing that Ni/Au is not stable on β-Ga2O3 at these temperatures. Photoluminescence revealed a decrease in total emission intensity in the near band-edge region after the introduction of etch damage. Electron beam-induced current measurements showed a decrease in the minority carrier diffusion length from 350 μm in the control sample to 311 μm in the etched sample.

In this thesis, liquid phase oxidation (LPO) on enhancement-mode AlGaAs/InGaAs metal-oxide-semiconductor pseudomorphic high electron mobility transistor (MOS-PHEMT) has been demonstrated. LPO was used on the GaAs cap layer to replace the traditional gate-recess process of the cap layer to further reduce the surface state and simplify the process. The maximum drain current density of 184 mA/mm, the maximum peak transconductance is 154 mS/mm at the VDS = 2 V, two-terminal diode of the reverse breakdown voltage is -25 V for MOS-PHEMT. Microwave characteristics and low-frequency noise are also better than those of the referenced case.

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Controlled n-type doping down to 2 × 1015 cm−3 was achieved in GaN grown on sapphire by MOCVD by balancing the n-type Si doping with respect to the background carbon and oxygen levels. A dopant level of ∼1 × 1016 cm−3 displayed a very high mobility of 899 cm2 V−1 s−1. High electron mobility in the drift layer leads to a low on resistance and high current densities without compromising on any other properties of the device. Schottky diodes processed on these low n-type layers showed low Ron values, while the p–n diodes display high reverse breakdown voltages in excess of 1000 V for 8 μm thick drift layers with a doping of 2 × 1015 cm−3.

The degradation of perovskite solar cells due to reverse bias (RB) is one of the remaining challenges hindering the commercialization of the technology. To overcome this challenge, a thorough understanding of and control over the breakdown (BD) voltage are crucial. A prerequisite for this is that the community “speaks the same language,” that is, that the reported BD voltages are comparable. A review of literature data shows that the impact of measurement parameters is often unknown and seems to depend strongly on sample properties. It follows that standardization is the only way to reach comparability. Here, a set of measurement parameters to fill this gap is proposed. Additionally, various definitions of a “BD voltage” are used in parallel without any way of relating them to each other; this metric and its determination need to be considered as well. After a thorough discussion of the available definitions, the use of the point of maximum curvature is introduced. Its main advantage is the possible connection to an analytical description of the BD mechanism. In this way, a starting point for scientists new to the field of RB stability is provided, and the ground for a broader discussion in the community is prepared.

The blocking voltage in diode (i.e., PN junction) using neutron-transmutation-doped Si can be improved by a field oxide annealed in N2O. It is experimentally determined that the reverse breakdown voltage is clearly increased although the ideality factor and leakage current density increase slightly. The improvement of blocking voltage may be due to the replacement of strained Si–O bonds by Si–N bonds in the field oxide and/or the relaxation of SiO2/Si interfacial strain. The increase of the ideality factor and leakage current for N2O-annealed devices might be attributed to the increase of SiO2/Si interface states.

Ga2O3 dielectric thin films were deposited on (111)-oriented p-type silicon wafers by plasma-enhanced atomic layer deposition using trimethylgallium and oxygen plasma. Structural analysis of the Ga2O3 thin films was carried out using grazing-incidence x-ray diffraction. As-deposited films were amorphous. Upon postdeposition annealing at 700, 800, and 900 °C for 30 min under N2 ambient, films crystallized into β-form monoclinic structure. Electrical properties of the β-Ga2O3 thin films were then investigated by fabricating and characterizing Al/β-Ga2O3/p-Si metal–oxide-semiconductor capacitors. The effect of postdeposition annealing on the leakage current densities, leakage current conduction mechanisms, dielectric constants, flat-band voltages, reverse breakdown voltages, threshold voltages, and effective oxide charges of the capacitors were presented. The effective oxide charges (Qeff) were calculated from the capacitance–voltage (C-V) curves using the flat-band voltage shift and were found as 2.6 × 1012, 1.9 × 1012, and 2.5 × 1012 cm−2 for samples annealed at 700, 800, and 900 °C, respectively. Effective dielectric constants of the films decreased with increasing annealing temperature. This situation was attributed to the formation of an interfacial SiO2 layer during annealing process. Leakage mechanisms in the regions where current increases gradually with voltage were well fitted by the Schottky emission model for films annealed at 700 and 900 °C, and by the Frenkel–Poole emission model for film annealed at 800 °C. Leakage current density was found to improve with annealing temperature. β-Ga2O3 thin film annealed at 800 °C exhibited the highest reverse breakdown field value.

An analytic solution of the two-dimensional poisson equation and a model of gate current and breakdown voltage for reverse gate-drain bias in GaAs MESFETs