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

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/cm² and 0.3–2 ms 2000 A/cm² 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/cm², and a reasonable good one for peak current densities up to 2000 A/cm² (1.2 ms current pulses).     

Simulation and experimental results on the forward J–V characteristic of Al implanted 4H–SiC p–i–n diodes

In this work the forward J–V characteristics of 4H–SiC p–i–n diodes are analysed by means of a physics based device simulator tuned by comparison to experimental results. The circular devices have a diameter of 350 μm. The implanted anode region showed a plateau aluminium concentration of 6×10¹⁹ cm⁻³ located at the surface with a profile edge located at 0.2 μm and a profile tail crossing the n-type epilayer doping at 1.35 μm. Al atom ionization efficiency was carefully taken into account during the simulations. The final devices showed good rectifying properties and at room temperature a diode current density close to 370 A/cm² could be measured at 5 V. The simulation results were in good agreement with the experimental data taken at temperatures up to about 523 K in the whole explored current range extending over nine orders of magnitude. Simulations also allowed to estimate the effect of a different p⁺ doping electrically effective profile on the device current handling capabilities.     

High power 875 nm Al-free laser diodes

Data are presented on Al-free InGaAsP-GaAs single quantum well laser diodes operating at 875 nm. Total output powers in excess of 4 W are achieved from a 100 μm broad area gain-guided device. Threshold currents under 200 A/cm² are reported for diodes operated continuous wave (cw) at room temperature (20°C)     

Characteristics of inversion-channel and buried-channel MOS devicesin 6H-SiC

Inversion-channel and buried-channel gate-controlled diodes and MOSFET's are investigated in the wide bandgap semiconductor 6H-SiC. These devices are fabricated using thermal oxidation and ion implantation. The gate-controlled diodes allow room temperature measurement of surface states, which is difficult with MOS capacitors due to the 3 eV bandgap of 6H-SiC. An effective electron mobility of 20 cm²/Vs is measured for the inversion-channel devices and a bulk electron mobility of 180 cm²/Vs is found in the channel of the buried-channel MOSFET. The buried-channel transistor is the first ion-implanted channel device in SIC and the first buried-channel MOSFET in the 6H-SiC polytype     

Effects of ionization rates on IMPATT device admittance

The significance of using different ionization rates on the operating characteristics of Si IMPATT devices is examined. The dc breakdown and small-signal results of IMPATT devices at room temperature are presented. Numerical results for p⁺nn⁺as well as the complementary n⁺pp⁺Si diodes in the millimeter-wave frequency range and at different current densities ranging from 2500 to 10 000 A/cm²are given. It is shown that large differences in some important device parameters are obtained, depending on the ionization rates employed.     

Experimental characterization of most''s scaled down to the 1 μm level

Fundamental MOS device performances are experimentally analyzed for the projected three levels of scaled-down, silicon-gate devices envisioned in the next decade. The final third-level device having 20 nm thick gate oxide and 0.7 μm effective channel length will have vertical dimension only 0.35 times that of the present 3 μm lithography level. Principal device characteristics discussed are threshold voltage, source to drain breakdown voltage, and effective carrier mobility under practical applied voltage conditions, mainly for dynamic MOS memory operation.

It is found that breakdown voltage reduction is the main obstacle hindering down-scaling, and also that the mobility lowering in the shorter channel length region reduces the merits of down-scaling. MOS device performances for the coming 1 μm geometry level LSI's under practical operation conditions are discussed on the basis of the experimental results obtained.     

Improved molecular beam epitaxial growth of AlxGa1 - xAs/GaAs high-radiance LED's for optical communications

We report some improvements made in molecular beam epitaxial growth of AlxGa1-xAs/GaAs high-radiance LED's for optical communications. These improvements have been achieved by growing these wafers in a system which includes an air-lock wafer-exchange chamber. Interfacial recombination velocity as low as6 times 10^{2}cm/s was obtained. The series resistance of the Burrus-type LED's was reduced by increasing the acceptor concentrations in the p-layers to a density as high as 10¹⁹cm^-3using Be as the dopant. CW output of 5.8 mW, or a radiance of 92 W/sr. cm², at a safe operating current of 150 mA has been obtained in these devices. The device performance is comparable to the best obtained in LPE-grown diodes of the same geometry.     

Electrical characteristics of GaAsP Schottky barrier diodes

Schottky barrier diodes of chromium on n-type epitaxial gallium arsenide phosphide (GaAsP) were studied from 25°C to 440°C. The diodes showed significant rectification properties up to a temperature of 440°C. At high temperature the reverse leakage current was 1.15 mA at 25 V with a diode area of 1.14×10⁻³ cm² as compared with 0.25-μA current at room temperature. The n factor derived from the slope of the ln I vs. V curves was 1.1. The barrier height for chromium was found to be 1.25 eV from the capacitance measurements and 1.12 eV from the saturation current vs. temperature measurements. The slope of the C-V curves yielded a carrier concentration of 6.0×10¹⁵ carriers per cm³.     

Hydrogen “doped” thin film diamond field effect transistors for high power applications

Early predictions that diamond would be a suitable material for high performance, high power devices were not supported by the characteristics of diodes and field effect transistors (FETs) fabricated on boron doped (p-type) thin film material. In this paper commercially accessible polycrystalline thin film diamond has been turned p-type by the incorporation of near surface hydrogen; mobility values as high as 70 cm² V⁻¹ s⁻¹ have been measured for films with a carrier concentration of 5×10¹⁷ cm⁻³. Schottky diodes and metal–semiconductor FETs (MESFETs) have been fabricated using this approach which display unprecedented performance levels; diodes with a rectification ratio >10⁶, leakage currents <1 nA, no indication of reverse bias breakdown at 100 V and an ideality factor of 1.1 have been made. Simple MESFET structures that are capable of switching V_DS values of 100 V with low leakage and current saturation (pinch-off) characteristics have also been fabricated. Predictions based upon experiments performed on these devices suggest that optimised device structures will be capable of operation at power levels up to 20 W mm⁻¹, implying that thin film diamond may after all be an interesting material for power applications.     

MOSFET Characteristics in low-temperature plasma-enhanced chemical vapor deposited epitaxial silicon

The fabrication of high-quality MOSFET's using low-temperature (750-800°C) Plasma-Enhanced Chemical Vapor Deposited (PECVD) epitaxial silicon is reported here for the first time. The fabricated devices include PMOS transistors with hole channel mobilities of 213 cm²/V.s (versus 218 cm²/V.s in bulk silicon controls) and NMOS transistors with electron channel mobilities of 520 cm²/V.s (versus 560 cm²/V.s in bulk silicon controls), and with an on-current to off-current ratio of 10⁷. These results indicate that epitaxial silicon films deposited by the PECVD technique are of high quality, even though the epitaxial deposition temperature was only 750-800°C.     

High-quality stacked CMOS inverter

A stacked CMOS technology with enhanced device performance and small geometries is discussed. Surface-channel mobilities were measured to be 700 cm²/V-s for bulk n-channel devices and 165 cm² /V-s for the top PMOS transistors. Excellent subthreshold slope of 100 mV/decade and leakage currents below 150-fA/μm channel width were measured for both device types. The low-impurity crystalline silicon film on top of the bulk devices was produced by local epitaxial overgrowth, an important alternative to recrystallized silicon films for three-dimensional CMOS circuits. The structure is planarized and requires only size masks with reduced processing time     

Reliability considerations for recent Infineon SiC diode releases

Silicon carbide (SiC) has long been shown to be one of the most promising materials for high-voltage power semiconductor devices. New device technologies and products have lead to an ever increasing size and variety of the markets addressed by SiC. The specific material properties and the new applications served by SiC devices give rise to specific reliability requirements, reaching beyond the scope of standard tests established for silicon based devices. Here, we show details of Infineon’s strategy to ensure high device reliability even under extreme operating conditions encountered in the field. E.g., an especially tailored dynamic reverse bias test shows that Infineon’s new 1200 V SiC Schottky diodes can be continuously operated at high voltage slopes of 120 V/ns under the conditions specified in this paper.     

Comparison of the aging behavior of diffused and epitaxial GaAlAs heterojunction electroluminescent diodes

Two Types of GaAlAs heterojunction electroluminescent diodes are compared. In the planar-type diffused diode the p-n homojunction is obtained by zinc diffusion in areas limited by a silicon nitride mask; the p-p heterojunction confines electrons in the bulk and avoids surface recombinations. The epitaxial diode is a conventional double heterojunction; the active area is limited by proton bombardment. The aging behaviors of these two types appear quite different. Diffused diodes degrade relatively fast; under continuous operation at 550 A/cm²(100 mA) the device lifetime (emitted light power falling down to 50 percent of the initial value) is 10 000 to 50 000 h. Epitaxial diodes degrade much more slowly; their device lifetime is estimated at several 10⁵h. The degradation is followed during aging, by using electrical and optical measurements, together with SEM and TEM analyses. It is confirmed that fast degradation occurs with simultaneous growth of dark line defects (DLD) and that these DLD's result from dislocation dipoles of interstitial nature, emitted either from scratches or, more frequently, from previously existing dislocations. It is shown that epitaxial diodes are practically free of dislocations; on the contrary, in the case of planar-type p-n junctions, a large number of dislocation loops are developed at the junction periphery, resulting from the mechanical stress at the edge of the junction during processing. This is the main source of DLD's and fast degradation of planar-type diffused diodes.     

Efficient GaAs---Ga1−xAlxAs heterostructure electroluminescent diodes

The development of efficient GaAs(Zn) electroluminescent diodes using a GaAs---Ga_1−xAl_xAs single heterostructure design is reported. External equantum efficiencies (300°K) of 10 per cent have been achieved at 9100 Å (1.36 eV) with pulsed current densities at and above 70 A/cm² on square diodes embedded in epoxy domes. The heterostructure consists of a Ga_1−xAl_xAs (Zn) p-layer grown by liquid phase epitaxy on an n-type GaAs substrate with the simultaneous diffusion of Zn a distance of 2 μm into the substrate. Several features of the heterostructure design contribute to the high efficiency: (1) the 9100 Å emission suffers little absorption in the Ga_1−xAl_xAs, (2) there is little nonradiative recombination at the GaAs---Ga_1−xAl_xAs interface, and (3) the compensated p-region produces 9100 Å radiation whichi s not strongly absorbed in the n-GaAs regions of the device. The external quantum efficiencies obtained with the heterostructure devices are nearly an order of magnitude higher than those obtained from conventional Zn-diffused GaAs homostructure diodes with similar geometry. The solution growth, fabrication, and electroluminescence properties of the heterostructure diodes are described.     

Breakdown degradation associated with elementary screw dislocations in 4H-SiC pn junction rectifiers

It is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vector>2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector=1c with no hollow core) in densities on the order of thousands per cm², nearly 100-fold micropipe densities. This paper describes an initial study into the impact of elementary screw dislocations on the reverse-bias current–voltage (I–V) characteristics of 4H-SiC p⁺n diodes. First, synchrotron white beam X-ray topography (SWBXT) was employed to map the exact locations of elementary screw dislocations within small-area 4H-SiC p⁺n mesa diodes. Then the high-field reverse leakage and breakdown properties of these diodes were subsequently characterized on a probing station outfitted with a dark box and video camera. Most devices without screw dislocations exhibited excellent characteristics, with no detectable leakage current prior to breakdown, a sharp breakdown I–V knee, and no visible concentration of breakdown current. In contrast, devices that contained at least one elementary screw dislocation exhibited 5–35% reduction in breakdown voltage, a softer breakdown I–V knee, and visible microplasmas in which highly localized breakdown current was concentrated. The locations of observed breakdown microplasmas corresponded exactly to the locations of elementary screw dislocations identified by SWBXT mapping. While not as detrimental to SiC device performance as micropipes, the undesirable breakdown characteristics of elementary screw dislocations could nevertheless adversely affect the performance and reliability of 4H-SiC power devices.     

In-situ low energy BF2+ion doping for silicon molecular beam epitaxy

An experimental study of the p-type ion dopant BF2+ in silicon molecular beam epitaxy (MBE) is described. BF2+ was used to dope MBE layers during growth to levels ranging from 1 × 10¹⁶/cm³to 4 × 10¹⁸/cm³over a growth temperature range of 650°C to 1000°C. The layers were evaluated using spreading resistance, chemical etching, and secondary ion mass spectroscopy. Complete dopant activation was observed for all growth temperatures. Remnant fluorine in the epitaxial layer was less than 2 × 10¹⁶/cm³in all cases. Diffused p-n junction diodes fabricated in BF2+-doped epitaxial material showed hard reverse breakdown characteristics.     

Uniformity and high temperature performance of X-band nitride power HEMTs fabricated from 2-inch epitaxy

X-band performance, high temperature D.C. operation and uniformity have been evaluated for 1 μm gate AlGaN/GaN HEMTs grown by RF atomic nitrogen plasma MBE. Deposition and fabrication were performed on 2-inch (0001) sapphire substrates to determine process uniformity. HEMTs with 300 μm total gate width and dual gate finger geometry have been fabricated with 650–700 cm² V⁻¹×s mobility. Maximum frequency cut-offs on the order of 8–10 GHz were achieved. D.C. performance at room temperature was >500 mA mm⁻¹, and external transconductance was >70 mS mm⁻¹. The transistors operated at test temperatures of 425°C in air.     

Experimental determination of electron drift velocity in 4H-SiC p+-n-n+ avalanche diodes

4H-SiC p⁺-n-n⁺ diodes of low series resistivity (<1×10^-4 Ω·cm²) were fabricated and packaged. The diodes exhibited homogeneous avalanche breakdown at voltages U_b=250-270 V according to the doping level of the n layer. The temperature coefficient of the breakdown voltage was measured to be 2.6×10^-4 k^-1 in the temperature range 300 to 573 K. These diodes were capable of dissipating a pulsed power density of 3.7 MW/cm² under avalanche current conditions. The transient thermal resistance of the diode was measured to be 0.6 K/W for a 100-ns pulse width, An experimental determination of the electron saturated drift velocity along the c-axis in 4H-SIC was performed for the first time, It was estimated to be 0.8×10⁷ cm/s at room temperature and 0.75×10⁷ cm/s at approximately 360 K     

High-power and low-threshold-current operation of 1.3 μm strain-compensated AlGaInAs/AlGaInAs multiple-quantum-well laser diodes

Low-threshold-current and high-temperature operation of 1.3 μm wavelength AlGaInAs/AlGaInAs strain-compensated multiple-quantum-well laser diodes (LDs) with a linearly graded index separate confinement heterostructure also made up of AlGaInAs has been successfully fabricated. The threshold current density and differential quantum efficiency are 400 A/cm² and 22% for the as-cleaved broad-area LDs with a 900 μm cavity length, respectively. The calculated internal quantum efficiency, internal optical loss, and threshold gain are 23%, 6.5 cm⁻¹, and 45 cm⁻¹, respectively. The threshold current and slope efficiency at room temperature for the 3 μm-ridge-stripe LDs without facet coating are 12 mA and 0.17 W/A, respectively. The peak wavelength is at 1295 nm with an injection current of 60 mA. With increasing the temperature up to 100 °C, the threshold current will increase up to 41 mA. The characteristic temperature is around 78 K in the range from 20 to 60 °C and 56 K in the range from 60 to 100 °C. The wavelength swing varied with temperature is 0.43 nm/°C for the LDs operated at 60 mA and room temperature.     

High-power 2.0 μm InGaAsP laser diodes

Data detailing the performance of strained-layer InGaAs/InGaAsP double-quantum-well laser diodes operating at 2.0 μm are presented. The total external efficiency and maximum power achieved are 55% and 1.6-W continuous wave (CW), respectively, from a 200-μm gain-guided laser diode. Measurements on gain-guided broad area devices yield an internal efficiency of 0.73 with a distributed loss coefficient, α, of 7.5 cm^-1. The measured threshold current density is 300 A/cm² for a 2-mm-long broad area device operated CW at 25°C