N. Papanicolaou

Pt and PtSix Schottky contacts on n‐type β‐SiC

Schottky barrier rectifying contacts using e‐beam‐deposited platinum have been demonstrated on n‐type β‐SiC. The electrical properties of these contacts were examined as a function of annealing temperature using I‐V and C‐V measurements. Auger analysis was used to study the metallurgical reactions at the Pt/SiC interface. Short annealing cycles in the 350–800 °C temperature range led to formation of a mixed structure of PtSix and PtC at the interface, evidenced by migration of platinum into the SiC above 350 °C. The barrier height was found to increase from 0.95 to 1.35 eV with increasing annealing temperature. The rectifying characteristics improved following an initial 350 °C anneal and remained relatively stable up to 800 °C.

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...

Material and n-p junction properties of N-, P-, and N/P-implanted SiC

Elevated temperature (ET) multiple energy N, P, and N/P implantations were performed into p-type 6H-SiC epitaxial layers. For comparison, room temperature (RT) N and P implantations were also performed. In the N/P coimplanted material a sheet resistance of 2.1×102 Ω/□ was measured, which is lower compared to the values measured in N or P implanted material of the same net donor dose. The RT P implantation resulted in heavy lattice damage and consequently low P electrical activation, even after 1600 °C annealing. After annealing the Rutherford backscattering yield either coincided or came close to the virgin level for ET implantations and RT N implantation, whereas for RT P implantation the yield was high, indicating the presence of high residual damage. Vertical n-p junction diodes were made by selective area ET N, P, and N/P implantations and RT N and P implantations using a 2.5 μm thick SiO2 layer as an implant mask. The diodes were characterized by capacitance–voltage and variable temperature current–v...

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...

Photonic microharp chemical sensors

We describe a new class of micro-opto-mechanical chemical sensors: A photonic microharp chemical sensor is an array of closely spaced microbridges, each differing slightly in length and coated with a different sorbent polymer. They are optically interrogated using microcavity interferometry and photothermal actuation, and are coupled directly to an optical fiber. Simultaneous measurements of the fundamental flexural resonant frequency of each microbridge allow the real-time detection and discrimination of a variety of vapor-phase analytes, including DMMP at concentrations as low as 17 ppb.

Sb-Based n- and p-Channel Heterostructure FETs for High-Speed, Low-Power Applications

Heterostructure field-effect transistors (HFETs) composed of antimonide-based compound semiconductor (ABCS) materials have intrinsic performance advantages due to the attractive electron and hole transport properties, narrow bandgaps, low ohmic contact resistances, and unique band-lineup design flexibility within this material system. These advantages can be particularly exploited in applications where high-speed operation and low-power consumption are essential. In this paper, we report on recent advances in the design, material growth, device characteristics, oxidation stability, and MMIC performance of Sb-based HEMTs with an InAlSb upper barrier layer. The high electron mobility transistors (HEMTs) exhibit a transconductance of 1.3S/mm at VDS=0.2V and an fTLg product of 33GHz-μm for a 0.2μm gate length. The design, fabrication and improved performance of InAlSb/InGaSb p-channel HFETs are also presented. The HFETs exhibit a mobility of 1500cm2/V-sec, an fmax of 34GHz for a 0.2μm gate length, a threshold voltage of 90mV, and a subthreshold slope of 106mV/dec at VDS=-1.0V.

Compensation implants in 6H–SiC

In this work, we have performed Si and C isoelectronic implantations in n-type and vanadium (V) implantations in p-type 6H–SiC to obtain highly resistive regions. The compensation is achieved by the lattice damage created by the Si and C implantations and the chemically active nature of the V implant. For the Si and C implantations, the as-implanted resistivity initially increased with increasing implant fluence due to the introduction of compensating levels caused by the lattice damage, then decreased at higher fluences due to hopping conduction of the trapped carriers. The resistivity of the Si and C implanted material has been measured after isochronal heat treatments over the temperature range of 400–1000 °C. The maximum resistivity values measured for Si and C implanted and heat treated material were ∼1012 Ω cm. For the 700 °C V implantation in p-type SiC, resistivities of >1012 Ω cm were measured after 1500 or 1600 °C annealing to activate the V implant. Redistribution of the V implant is observed a...

Planar fully ion implanted InP power junction FET's

This letter reports on the fabrication and performance of planar all ion-implanted 1.0-µm gate length InP power junction field effect transistors (JFETs). The devices were fabricated utilizing n+ implantation, a AuZn/TiW/Au gate metallization, and an n+ drain ledge. At 4.5 GHz, the 300-µm gate width JFETs exhibited maximum insertion gains of up to 13 dB and scaled output powers as high as 1 W/mm with 3-dB gain.

In0.53Ga0.47As metal‐semiconductor‐metal photodetector using proton bombarded p‐type material

Metal‐semiconductor‐metal (MSM) photodetectors have been fabricated using as‐grown and proton‐bombarded p‐type In0.53Ga0.47As. Proton bombardment caused a decrease in the dark current, an increase in the breakdown voltage, and an improvement in the speed of the MSM detector. The dark current of the MSM detector with 3×1015 cm−3 proton bombardment is 10 nA at 2 V and 300 nA at 5‐V bias. The dc responsivity is 0.7 A/W and impulse response full width at half maximum is 160 ps for 1.3 μm radiation at 5 V bias.