Christian Brylinski

Barrier inhomogeneities and electrical characteristics of Ti/4H-SiC Schottky rectifiers

Forward density-voltage (J-V) measurements of titanium/4H-SiC Schottky rectifiers are presented in a large temperature range. While some of the devices present a behavior in accordance with the thermionic current theory, others present an excess forward current at low voltage level. This anomaly appears more or less depending on the rectifier and on the temperature. A model based on two parallel Schottky rectifiers with different barrier heights is presented. The characteristics show good agreement. It is shown that the excess current at low voltage can be explained by a lowering of the Schottky barrier in localized regions. A proposal for the physical origin of these low barrier height areas is given.

Growth of ultrapure and Si‐doped InP by low pressure metalorganic chemical vapor deposition

Low pressure metalorganic chemical vapor epitaxial growth and characterization of high purity and Si‐doped indium phosphide on semi‐insulating (100) InP:Fe substrate are presented in this letter. Electrical characteristics of the layers were determined from Hall measurements. Hall mobilities as high as 145 000 cm2 V−1 s−1 at 77 K have been achieved on high purity layers with net donnor density ND−NA≂2×1014 cm−3. High resolution photoluminescence measurements were performed with the as‐grown layers at temperatures down to 1.7 K. Carrier concentration and the resulting mobility of intentionally Si‐doped low pressure metalorganic chemical vapor deposition grown InP layers were also studied.

SiO2/6H-SiC(0001)3×3 initial interface formation by Si overlayer oxidation

We investigate the initial oxidation and SiO2/6H-SiC interface formation by core level photoemission spectroscopy using synchrotron radiation. The results indicate that the direct oxidation of the 6H–SiC(0001)3×3 surface leads to SiO2 formation at low temperatures (500 °C) with a nonabrupt interface having significant amounts of mixed (Si–O–C) and intermediate (Si3+,Si2+,Si+) oxidation products. In contrast, C-free and a much more abrupt SiO2/6H-SiC(0001) interface formation is achieved when predeposited Si overlayer is thermally oxidized at low oxygen exposures and low temperatures (500 °C).

Self-heating effects in silicon carbide MESFETs

Silicon carbide materials offer specific advantages to MESFET applications. However, to put them to good use requires to apply higher drain voltages than in GaAs devices. Therefore, in spite of the high thermal conductivity of the SiC substrates, this leads to a large power dissipation and a substantial increase in the local temperature. Depending on the device configuration, this self-heating can induce a negative differential conductance at very low frequency near dc regime. A simple analytical model is proposed, which yields a reasonable fit of the MESFET static characteristics. Further experimental evidence for such effects is also given, which corroborates the predictions of the model.

Characterization of ohmic and Schottky contacts on SiC

The interface chemistry of nickel and tungsten based contacts on SiC has been investigated by XPS on as-deposited samples and after contact formation. After annealing at 950 °C for 10 min, Ni/SiC and Ni/Si/SiC ohmic contacts are formed due to the chemical reactions, as a result of which Ni2Si appears. However, Ni/Si (instead of pure Ni) deposition on SiC leads to modification of the diffusion processes and formation of a contact layer free of carbon. After annealing at 1200 °C for 4 min, the WN (W)/SiC systems are characterized by strong interface reactions resulting in W5Si3 and W2C formation in the contact layer. The 800 °C annealed WN/SiC contact is characterized by a chemically inert interface, and is found to be of a Schottky type.

Progress in the use of 4H-SiC semi-insulating wafers for microwave power MESFETs

Abstract The use of Silicon Carbide semi-insulating wafers has to be mastered in order to reach output power densities up to 3–4 W mm−1 in the 1–2 GHz frequency range (values that are currently targeted). This study shows that the buffer layer doping level and thickness have a great influence on the MESFET behavior. We have studied three epilayer configuration on SI substrates that differ only by the buffer layer. On two of them, a slow drain current decrease in d.c. mode was observed. On the third one, no d.c. current drift was observed without rf input power, but drain current decreases instantaneously when rf input power is switched on. Traps, located either in the buffer layer or in the substrate are supposed to be responsible for these drift phenomena. Load–pull measurements were performed at 2 GHz on transistors fabricated on the three different structures. One of them, with a 2 mm gate periphery, has been measured under 72 V drain–source bias voltage and 2.1 W mm−1 power density was obtained at 2 GHz. We believe these results are the first to be published on a SiC MESFET with d.c. bias voltage over 70 V.

Electrical characterization of inhomogeneous Ti/4H-SiC Schottky contacts

Abstract Forward I ( V ) measurements of Titanium/4H–SiC Schottky rectifiers are presented in a large temperature range. Significant dispersion is observed on the room temperature characteristics. Some of the rectifiers show good agreement with the thermionic model. Other samples present excess current at low voltage level. For these rectifiers we have been able to fit the experimental characteristics assuming the coexistence of low and high barrier height areas. In this model, the forward current results from the addition of the thermionic currents provided by the two parallel diodes. Forward I ( V ) measurements as a function of temperature have been performed from 100 to 600 K. On a given diode, a transition between one barrier and two barriers behaviours can be evidenced as temperature changes. Variations in the calculated barrier height and ideality factor are therefore evidenced. It is shown that the excess current at low voltage depends on the ratio of the low Schottky barrier region over the total diode area. Material inhomogeneity is one possible explanation for the existence of inhomogeneous barrier height on the Ti/4H–SiC contact.

Ga1−xInxAs/InAsyP1−y/InP photodiodes for the 1.6 to 2.4 μm spectral region grown by low pressure MOCVD

Abstract Photodiodes with a cut-off wavelength extended in the infrared-region up to 2.4 μm have been fabricated using a mismatched Ga 1- x In x As/InAs y P 1- y /InP double heterostructure prepared by the low pressure MOCVD epitaxial technique on InP substrate. The ternary composition Ga 0.2 In 0.8 As was chosen to tailor the bandgap of the Ga 1- x In x As absorption layer to long wavelength detector requirements. An InAs y P 1- y ( y = 0.5) graded composition layer followed by an (InAs y P 1- y /Ga 1- x In x As) superlattice acting as a barrier to dislocation propagation has been used to accommodate the 1.8% lattice mismatch between the InP substrate and the Ga 0.2 In 0.8 As active layer of the device. Room temperature typical dark current I d of the PIN photodiode at -1 V reverse bias, is about 8x10 -4 A/cm 2 .

Long-term reliability of Ti–Pt–Au metallization system for Schottky contact and first-level metallization on SiC MESFET

Abstract The stability of metal layers on semiconductors is a key issue for the device electrical performances. Therefore, the reliability of SiC/Ti/Pt/Au system was investigated using storage steady-stress testing, AES (Auger Electron Spectrometry), and SIMS (Secondary Ions Mass Spectrometry) analysis. The study was conducted on different patterns for gate and interconnection structure to underline the different reliability problems. Auger and SIMS analysis showed important modifications in the three-metal structure without reactions with the SiC substrate. The resistance degradation was assigned to interdiffusion phenomena. It was analyzed with a diffusion-controlled model. Activation energies and mean time to failure (MTF) were calculated for a failure criterion defined as a 10% increase of the resistance. Finally, the different rules of the metallization degradation in MESFET behaviours for interconnections and gate were discussed.

Power GaInP/GaAs HBT MMICs

GaInP/GaAs HBT technology is an excellent alternative to GaAlAs/GaAs HBTs. We present new X-Band power results both on discrete devices and on MMICs obtained using this new type of HBT. 12-2×30-¿m2 finger discrete devices show an output power of 1W at 10 GHz with a power added efficiency of 43% under near class A bias conditions. The dependence of the power gain on the HBT topology has been simulated and that predicts precisely the device performances. First power amplifier MMICs have been produced by Thomson-CSF. Those MMIC amplifiers achieve an output power above 1 W at 10 GHz under both CW and pulsed conditions. The power gain is higher than 12dB at 10 GHz. At the same RF frequency, the power added efficiency reaches 35% and 25% under pulsed conditions (3 ¿s, 10% duty cycle) and CW respectively. These first results are promising, and improved results are expected soon by tuning the output matching network and using higher gain devices.