Bo Breitholtz

Application of optical emission microscopy for reliability studies in 4H–SiC p+/n−/n+ diodes

An optical emission microscopy technique with spatial and spectral resolution capabilities is applied for stability studies of 4H–SiC material properties. From the example of a 4H–SiC p+/n−/n+ diode imaged at different stages of electrical overstress the mechanism of degrading performance is directly unveiled. We correlate this phenomenon with irreversible structural changes within the active region created by a nonuniform heating related stress. The stress-generated features are interpreted as multiple stacking faults spreading throughout the whole base region and nucleated in the vicinity of built-in defects and process-induced structural deficiencies.

Stable dynamic avalanche in Si power diodes

A stable dynamic avalanche at a maximum power density of about 2.4 MW/cm(2) was measured in small areas of 3.3 kV Si power diodes, using an optical measurement technique, and very good dynamic rugg ...

Dynamic avalanche in 3.3-kV Si power diodes

Measurements of the safe reverse recovery limit were performed for 3.3-kV Si power diodes using a novel optical experimental technique. In this experiment, influence of the junction termination is effectively eliminated by optical generation of a laterally-localized carrier plasma. The turn-off failures observed in measurements at two temperatures showed no temperature dependence and could not be reproduced in ordinary one-dimensional (1-D) or two-dimensional (2-D) device simulations. To simulate the stability of the current density toward current filamentation, two 1-D diodes with an area ratio 1:19 and a 10% difference in initial carrier plasma level, were simulated in parallel. This resulted in a strongly inhomogeneous current distribution, and a rapid reverse voltage fall resembling the measured turn-off failures. Inhomogeneous current distribution in these simulations appears as the current decay ceases due to impact ionization, in qualitative agreement with a current instability condition proposed by Wachutka [1991].

Heat generation in Si bipolar power devices : The relative importance of various contributions

Abstract According to existing theories, several effects contribute to the generation of heat in semiconductor devices, both in stationary and in transient processes. By performing within the drift-diffusion approximation simulations of a Si power diode during different operating conditions (turn-on, steady-state and turn-off), various contributions to the heat generation and temperature distribution have been calculated. It is found that Joule heat and recombination heat alone determine the lattice temperature distribution, even in strongly time-dependent processes. The operating conditions have been chosen such that these results should have a rather general validity.

TIME-RESOLVED IMAGING OF RADIATIVE RECOMBINATION IN 4H-SIC P-I-N DIODE

The time-resolved imaging of electron-hole recombination radiation from a forward-biased 4H–SiC p-i-n diode is reported. A novel approach of combining gated charge couple device technique with cross-sectional emission microscopy is demonstrated as a fast and informative method for characterization of both 4H–SiC material properties and the overall power device performance. We present the capability of the technique to visualize structural defects, to characterize spatial distribution and dynamics of injected carriers, and to provide effective carrier diffusion and lifetime parameters. From the results of lateral and in-depth imaging of the light emission we conclude that at low currents the injection of holes from the p+ emission is dominant. Furthermore, an effective carrier lifetime of 350 ns in the active n− region and a diffusion length of 15 μm in the substrate are readily obtained.

Space and time resolved surface temperature distributions in Si power diodes operating under self-heating conditions

Abstract In order to optimize and improve the design of power devices with improved surge current safe operating area it is necessary to obtain a good correlation between measured and simulated space and time resolved temperature distributions. Therefore, an IR microscope capable of measuring the space and time resolved surface temperature distributions in Si power diodes operating under self-heating conditions has been developed. The minimum detectable spot size is 15 μm, while the signal rise time is detector limited to about 1 μs. The lower temperature detectivity limit is about 10°C over room temperature. Using this instrument dynamic thermal phenomena in fast recovery 3.3 kV Si power diodes having radiation-induced recombination centers [Proceedings of the 7th EPE, Trondheim, 1997] subjected to 1.2 ms 400–2000 A/cm 2 and 0.3–2 ms 2000 A/cm 2 current pulses have been studied. The experimental results have been compared to results from 2D device simulations including surface recombination and carrier lifetime temperature dependence. The agreement between experimental and device simulation results (i.e. dynamic IV characteristics and time and space resolved temperature distributions) is very good up to a peak current density of 1500 A/cm 2 , and a reasonable good one for peak current densities up to 2000 A/cm 2 (1.2 ms current pulses).

Dynamic avalanche in Si power diodes and impact ionization at the nn + junction

The reverse recovery failure limit was measured with an optical technique for power diodes which sustain high levels of dynamic avalanche. Measurements and simulations indicate that these diodes wi ...

Simulation and electrical characterization of GaN/SiC and AlGaN/SiC heterodiodes

Heterojunctions on SiC is an area in rapid development, especially GaN/SiC and AlGaN/SiC heterojunctions. The heterojunction can improve the performance considerably for BJTs and FETs. In this work heterojunction diodes have been manufactured and characterized. The structure was a GaN or AlGaN n-type region on top of a 6H-SiC p-type substrate. Two different approaches of growing the n-type region were tested. The GaN was grown with the MBE technique using a polycrystalline GaN buffer, whereas the AlGaN was grown with CVD and an AlN buffer. The AlGaN had an aluminum mole fraction of around 0.1. Mesa structures were formed using Cl2 RIE of GaN/AlGaN, which showed good selectivity on 6H-SiC (about 1:6). A Ti metallization with subsequent RTA was used as contact to GaN and AlGaN, and the contact to 6H-SiC was liquid InGa. Both I-V and C-V measurements were performed on the heterojunction diode. The ideality factor of the diodes, doping concentration of the SiC, and the band alignment of the heterojunction were extracted. © 1999 Elsevier Science S.A.

Simulations and measurements of emitter properties in 5 kV Si PIN diodes

Emitter properties have been studied by comparing simulated and measured data of excess carrier concentration and surface potential in 5 kV Si PIN diodes. Comparison were made under forward conduction and turn-on for current densities in the range 30-300 A/cm/sup 2/ and for different depths and concentrations of the n/sup +/ and p/sup +/ emitters. The density of excess carriers were measured by the Free Carrier Absorption (FCA) technique as a function of depth and the surface potential by scanning a tungsten probe tip on the polished diode surfaces. The FCA measurements correlate well to simulated data, but discrepancies between simulated and measured data of the surface potential indicate the need for improved physical models.

Physical phenomena in Si power diodes operating at high carrier injection levels and high temperature

The physics of fast recovery 3.3 kV Si power diodes radiation induced recombination centers operating under forward bias at large current densities and high temperatures have been studied both experimentally and by means of computer simulations. In the experimental studies the dynamic I-V characteristics, the surface temperature and the surface potential distribution in the n-base have been measured, while the diodes were being subjected to single 1.3 ms half-sine-wave current pulses having a density in the range of 100 to 7200 A/cm/sup 2/. The experimental dynamic I-V characteristic curves obtained are rich in features and determined by the effects that temperature and carrier concentration have on the carrier mobility and lifetime, on the Fermi-Dirac distribution function and on the energy band gap. The experimental results have been used to check the validity of the physical models implemented in the simulation package AVANT! MEDICI. Simulations performed using the standard physical models implemented in MEDICI give an excellent agreement with measurement results up to a peak current density of 1500 Amps/cm/sup 2/, and a reasonable good one up to a peak current density of 2000 Amps/cm/sup 2/. However, the agreement between measurements and simulations is very poor at peak current densities above 2000 Amps/cm/sup 2/.