Avalanche Breakdown Field Research Articles

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.

Foreword Special Issue on Wide Bandgap Power Switching Devices for Energy Efficiency and Renewable Energy Integration

Wide bandgap (WBG) semiconductors, especially silicon carbide (SiC) and gallium nitride (GaN), promise transformational advances in electrical power systems, with increased power conversion efficiency for transportation and renewable energy utilization. Compared with the semiconductor silicon, SiC and GaN materials offer significantly higher electrical and thermal conductivities, increased avalanche breakdown field strength, and improved ruggedness under extreme environmental operating conditions. These basic material properties translate into more compact and lightweight power conversion systems with significant energy savings, much improved signal sensing and transmission characteristics, and longer operating life in the field.

Electric field induced avalanche breakdown and non-volatile resistive switching in the Mott Insulators AM4Q8

The Mott insulator compounds AM4Q8 exhibit a new type of volatile and non volatile resistive switchings that are of interest for RRAM application. We found that above a threshold electric field E TH of the order of a few kV/cm these compounds undergo a volatile resistive switching based on an avalanche process. For electric field much higher than the threshold avalanche breakdown field, the resistive switching turns non volatile. Our EDXS and STEM analyses show that the non volatile resistive switching originating from the avalanche breakdown can neither be ascribed to local chemical modifications nor to a local phase change with symmetry breaking at a resolution better than a few nanometer. This is in strong contrast with non volatile resistive switching reported so far that are all based on chemical or structural changes. Conversely, our results suggest that the avalanche breakdown induce the collapse of the Mott insulating state at the local scale and the formation of a granular conductive filament formed by compressed metallic domains and expanded “superinsulating” domains.

Introduction to the Focus Issue on Wide Bandgap Power Semiconductors

Wide bandgap (WBG) semiconductors, especially Silicon Carbide (SiC) and Gallium Nitride (GaN), offer unprecedented opportunities for transformative changes in electric utility and transportation infrastructures. Compared to semiconductor silicon, SiC and GaN offer significantly higher electrical and thermal conductivities, increased avalanche breakdown field strength, and improved ruggedness under extreme environmental operating conditions. These basic material properties translate into more compact and lightweight energy conversion systems with significant energy savings, much improved signal sensing and transmission characteristics, and longer operating lifetimes in the field. Commercial products that are poised to significantly benefit from SiC and GaN semiconductors include solid-state energy converters, power management electronics, power amplifiers, light-emitting diodes (LEDs), solar cells, lasers, and environmental sensors. The current global annual market potential for these products is collectively in excess of $100 billion. The potential annual market size for WBG power semiconductor devices alone now exceeds $30billionwithexponentialgrowthexpectedinthenextdecade.However, state-of-the-art commercial WBG power devices have limited voltage and current ratings, unproven field-reliability, and are prohibitively expensive. Consequently, the current global sales of WBG power devices is about $200 million per year. Realizing the current technology status and the vast commercial potential of WBG power semiconductor devices, an annual ECS Symposium on GaN and SiC Power Technologies was established in 2011. The2013Symposiumispoisedtobeveryexcitingandwillincludeoral presentations of more than 60 high-quality technical papers and two evening panel sessions involving in-depth discussion of topics ranging from materials to end-applications, and their inter-relationships, in order to understand and address the critical issues that are hindering rapid commercialization of WBG power technologies. Thisfocusissueincludesatotalof18full-lengthpeer-reviewedpapers. The focus issue begins with an overview paper that summarizes the current status and emerging trends in WBG power semiconductor devices from application considerations; the imminent need to reduce crystal defects in both bulk substrates and epitaxial layers is the highlight of this paper. There are a total of eight papers on SiC material technology.MorespecificallyonepaperonSiCbulksubstrategrowth, five papers on SiC homoepitaxy, one paper on SiC surface modification, and one paper on SiC material characterization. In addition, two papers on bulk GaN crystal growth and one paper on GaN-on-Si epitaxy are included. One paper deals with SiC and GaN wafer planarization,animportantprocessingtechniquepriortomaterialgrowth ∗ Electrochemical Society Active Member.

Pores in n-Type InP: A Model System for Electrochemical Pore Etching

The growth mechanism of currentline-oriented pores in n-type InP has been studied by Fast-Fourier-Transform Impedance Spectroscopy (FFT IS) applied in situ during pore etching and by theoretical calculations. Several pore growth parameters could thus be extracted in situ that are otherwise not obtainable. These include the space-charge-region (SCR) width, the SCR potential, the capacitance at the pore tips, and the avalanche breakdown field strength. It could be demonstrated that the system adjusts itself in such a way that the potential across the space-charge-region at the pore tips is kept constant within a certain bandwidth of the applied potential. This provides for a constant field strength at the pore tips, ensuring that avalanche breakdown occurs, generating the necessary holes for the electrochemical dissolution of InP.

Growth and Characterization of High-Performance GaN and AlxGa1−xN Ultraviolet Avalanche Photodiodes Grown on GaN Substrates

AbstractWide-bandgap III-nitride-based avalanche photodiodes (APDs) are important for photodetectors operating in UV spectral region. For the growth of GaN-based heteroepitaxial layers on lattice-mismatched substrates such as sapphire and SiC, a high density of defects is introduced, thereby causing device failure by premature microplasma breakdown before the electric field reaches the level of the bulk avalanche breakdown field, which has hampered the development of III-nitride based APDs. In this study, we investigate the growth and characterization of GaN and AlGaN-based APDs on free-standing bulk GaN substrates. Epitaxial layers of GaN and AlxGa1−xN p-i-n ultraviolet avalanche photodiodes were grown by metalorganic chemical vapor deposition (MOCVD). Improved crystalline and structural quality of epitaxial layers was achieved by employing optimum growth parameters on low-dislocation-density bulk substrates in order to minimize the defect density in epitaxially grown materials. GaN and AlGaN APDs were fabricated into 30μm- and 50μm-diameter circular mesas and the electrical and optoelectronic characteristics were measured. APD epitaxial structure and device design, material growth optimization, material characterizations, device fabrication, and device performance characteristics are reported.

Optimization of a SiC Super-SBD Based on Scaling Properties of Power Devices

Scaling theory is applied in the design of power devices. The scaling law for power devices is presented. A new figure of merit (HFOM) is derived as an invariant of scale transformation, which is a function of avalanche breakdown field and regarded as a measure of the performance of a power device. The optimization of a SiC Schottky barrier diode with the floating junction structure (Super-SBD) has been performed using the HFOM as a measure of the performance. The performance of the optimized Super-SBD surpasses the performance limit of 4H-SiC devices with the conventional structure.

Performance evaluation of picosecond high-voltage power switches based on propagation of superfast impact ionization fronts in SiC structures

We employ a simple analytical model of superfast impact ionization front in a reversely biased p+-n-n+ structure to evaluate the performance of prospective 4H-SiC closing switches based on propagation of ionization fronts. The model allows to relate the order of magnitude values of the front velocity and the electron-hole plasma concentration behind the front to the basic material and structural parameters. We show that high avalanche breakdown field and impact ionization rate of the wide-band-gap 4H-SiC lead to dramatic improvement of switching characteristics with respect to Si structures currently used in pulse power applications. The concentration of electron-hole plasma generated by the front passage is of the order of 1018 versus 1016cm−3 in Si. The velocity of ionization front in 4H-SiC is several times larger than in Si. Finally, we discuss possible triggering mechanisms for the ionization front in SiC.

Process and Device Simulation of a SiC Floating Junction Schottky Barrier Diode (Super-SBD)

This paper describes process and device simulation results of SiC floating junction Schottky barrier diodes (Super-SBDs). Two-dimensional process simulation of a SiC device is implemented using the customized ISE’s process simulator “DIOS”. The simulation results reproduce the experimentally observed buried floating junction structure of a SiC Super-SBD. The device simulation method using the anisotropic impact ionization coefficients is formulated. The effect of anisotropic avalanche breakdown field on termination structures of SiC SBDs is examined. Finally, by the device simulation we have shown that the trade-off between the on-state resistance and the breakdown voltage of the super-SBD that contains two drift layers exceeds that of the conventional SBD.

Donor avalanche breakdown field in n-GaAs: Effect of concentration and lattice temperature

A threshold avalanche breakdown field associated with the impact ionization of shallow donors by hot electrons in n-GaAs is calculated from the Boltzmann transport equation for various values of donor concentration, compensation ratio and lattice temperature. At low and moderate donor concentrations, N D < 10 15 cm −3, the results are in good agreement with the available experimental data. The curves on the avalanche breakdown field presented in this paper may be used in optimizing the operational characteristics of impurity-based cryogenic devices, such as far-infrared photomultipliers.

An approximate formula for the avalanche breakdown field in semiconductors

An approximate formula for the avalanche breakdown field in semiconductors