J.A. Mittereder

Improved reliability of AlGaN-GaN HEMTs using an NH/sub 3/ plasma treatment prior to SiN passivation

A passivation method has been developed which reduces the degradation of AlGaN-GaN high electron mobility transistor (HEMT) electrical properties caused by extended dc bias or microwave power operation. The key aspect of this passivation technique is exposure to a low-power NH/sub 3/ plasma prior to SiN deposition. Devices fabricated with the NH/sub 3/ treatment prior to SiN passivation show minimal gate lag and current collapse after extended dc bias operation. In addition, the rate of degradation of the microwave power output while under continuous microwave operation is improved by at least 100 times as compared to SiN passivated HEMTs that were not treated with the NH/sub 3/ plasma.

Current collapse induced in AlGaN/GaN high-electron-mobility transistors by bias stress

Current collapse is observed to be induced in AlGaN/GaN high-electron-mobility transistors as a result of short-term bias stress. This effect was seen in devices grown by both metalorganic chemical vapor deposition (MOCVD) and molecular-beam epitaxy (MBE). The induced collapse appears to be permanent and can be reversed by SiN passivation. The traps responsible for the collapse have been studied by photoionization spectroscopy. For the MOCVD-grown devices, the same traps cause the collapse in both unstressed and stressed devices. These effects are thought to result from hot-carrier damage during stress.

Ion-Implantation in Bulk Semi-Insulating 4H-SiC

Multiple energy N (at 500 °C) and Al (at 800 °C) ion implantations were performed into bulk semi-insulating 4H–SiC at various doses to obtain uniform implant concentrations in the range 1×1018–1×1020 cm−3 to a depth of 1.0 μm. Implant anneals were performed at 1400, 1500, and 1600 °C for 15 min. For both N and Al implants, the carrier concentration measured at room temperature for implant concentrations ⩽1019 cm−3 is limited by carrier ionization energies, whereas for the 1020 cm−3 implant, the carrier concentration is also limited by factors such as the solubility limit of the implanted nitrogen and residual implant damage. Lattice quality of the as-implanted and annealed material was evaluated by Rutherford backscattering spectroscopy measurements. Residual lattice damage was observed in the implanted material even after high temperature annealing. Atomic force microscopy revealed increasing deterioration in surface morphology (due to the evaporation of Si containing species) with increasing annealing t...

Effectiveness of AlN encapsulant in annealing ion-implanted SiC

Aluminum nitride (AlN) has been used as an encapsulant for annealing nitrogen (N), arsenic (As), antimony (Sb), aluminum (Al), and boron (B) ion-implanted 6H-SiC. Atomic force microscopy has revealed that the AlN encapsulant prevents the formation of long grooves on the SiC surface that are observed if the AlN encapsulant is not used, for annealing cycles up to 1600 °C for 15 min. Secondary ion mass spectrometry measurements indicated that the AlN encapsulant is effective in preserving the As and Sb implants, but could not stop the loss of the B implants. Electrical characterization reveals activation of N, As, Sb, and Al implants when annealed with an AlN encapsulant comparable to the best activation achieved without AlN.

Cr/Al and Cr/Al/Ni/Au ohmic contacts to n-type GaN

In this work we investigate the performance of Cr/Al and Cr/Al/Ni/Au ohmic contacts on n-type GaN. Annealing of the contacts was achieved by using a low temperature conventional quartz tube furnace in an Ar ambient and a new vacuum annealing technique using a tungsten strip heater. Low specific contact resistivity (ρc) metallizations were achieved with furnace annealing at considerably lower temperatures (550–600 °C) than those typically required for GaN contacts by halogen lamp rapid thermal annealing (∼900 °C). Vacuum annealing was found to require temperatures similar to those used in halogen lamp rapid thermal annealing for forming ohmic contacts on n-type GaN, but with minimal oxidation of the Al surface. For the Cr/Al bilayer on GaN with n doping of 1018 cm−3, minimum specific contact resistivities of 1.6×10−4 Ω cm2 and 2.3×10−5 Ωcm2 were achieved for furnace annealing and vacuum annealing, respectively. Our experiments showed that, when Cr was used as a contact material, the simultaneous presence o...

Metallization options and annealing temperatures for low contact resistance ohmic contacts to n-type GaSb

The quest for faster electronic devices combined with the requirement of low power dissipation has revived the interest in the near 6.1 /spl Aring/ lattice constant antimony containing III-V compounds. Among the known III-V semiconductors, InSb has the highest electron mobility and GaSb the highest hole mobility. In addition favorable bandgap alignments are predicted with related III-V ternaries and quaternaries suitable for high-speed heterostructure transistors, lasers, and optoelectronic devices. The device fabrication technology of antimony containing III-V compounds however, is in its infancy and considerable work needs to be performed. In this work, we report the development of a low contact resistance ohmic contacts for n-type GaSb suitable for heterostructure device applications, with over an order of magnitude improvement in contact resistance and specific contact resistivity. The MBE growth of Te doped n-type GaSb and crucial device processing and pre-metallization surface treatment will be discussed. A variety of metallization schemes containing Au, Ge, In, Ni, Pd, and Pt and the effects of annealing temperature are examined.

AlSb/InAs HEMTs with a TiW/Au gate metalization for improved stability

Abstract We report on the fabrication and characteristics of AlSb/InAs high electron mobility transistors (HEMTs) with a TiW/Au gate metalization. Using gate leakage and S -parameter measurements as a measure of stability, the HEMTs were found to be thermally stable up to 180 °C when heat treated in a H 2 /N 2 ambient.

Quantitative measurement of channel temperature of GaAs devices for reliable life-time prediction

The channel temperature of Gallium Arsenide (GaAs) devices was quantitatively measured using scanning thermal microscopy (SThM), which is a variation of atomic force microscopy (AFM). The temperature of the devices was also characterized by infrared (IR) imaging and thermal modeling. The measured SThM temperature values were close to the calculated values from the model, and were higher than those found by IR, as predicted. In contrast to most published AFM results which have reported only qualitative and indirect semi-quantitative thermal information about the sample, the results presented here can be used directly to determine accurately the device-temperature. These results are useful to the reliability community in that they help to predict a more accurate semiconductor device lifetime. By careful calibration of an AFM thermistor probe tip, a quantitative temperature measurement of the channel temperature of the GaAs PHEMTs and MESFETs can be made. The result of the measurement can be substantiated by applying a suitable thermal calculation, such as the Cooke model. A secondary measurement technique, such as IR microscopy, can also be useful in providing further information about the thermal response of the device. Published results using AFM techniques have been unable to determine the channel temperature quantitatively. The method in this paper applies to other types of electronic devices for which the channel (or junction) temperature can be probed from the top surface of the device.

Characteristics of planar n-p junction diodes made by double-implantations into 4H-SiC

Double implantation technology consisting of deep-range acceptor followed by shallow-range donor implantation was used to fabricate planar n/sup +/-p junction diodes in 4H-SiC. Either Al or B was used as the acceptor species and N as the donor species with all implants performed at 700/spl deg/C and annealed at 1650/spl deg/C with an AlN encapsulant. The diodes were characterized for their current-voltage (I-V) and capacitance-voltage (C-V) behavior over the temperature range 25/spl deg/C-400/spl deg/C, and reverse recovery transient behavior over the temperature range 25/spl deg/C-200/spl deg/C. At room temperature, the B-implanted diodes exhibited a reverse leakage current of 5/spl times/10/sup -8/ A/cm/sup 2/ at a reverse bias of -20 V and a carrier lifetime of 7.4 ns.

Measurement of Local Temperatures Using µ-Raman of SiC and AlGaN-GaN/SiC Power and RF Devices

Confocal μ-Raman was used to measure the operating temperatures in SiC MESFETS, AlGaN/GaN/SiC HEMT’s and 4H-SiC PiN diodes. Temperatures obtained from thermal imaging of the MESFETS compared well with those measured from Raman scattering. Operating temperatures were also obtained for large area PiN diode and it was shown that a single point at the center of the device can be used to measure the average temperature.