Seema Vinayak

Thermal reliability of n-GaAs/Ti/Pt/Au Schottky contacts with thin Ti films for reduced gate resistance

Abstract The thermal stability of Ti/Pt/Au Schottky contacts on n-GaAs with Ti films 0–60 nm is investigated. The contacts with Ti films as small as 10 nm remain thermally stable with annealing up to 400°C. The changes induced by thermal treatment in the electrical characteristics of the contacts are correlated with the Rutherford backscattering and microscopic analysis of the annealed samples. It shows profuse interdiffusion and interfacial reaction with 300°C anneal for the GaAs/Pt/Au system. It has been found that introducing the Ti film between GaAs and Pt/Au, the interdiffusion of Pt and Au is also prevented. These results are useful for reducing the gate metallisation resistance of metal semiconductor field effect transistors.

Studies on the Thermal Stability of Ni/n–GaN and Pt/n–GaN Schottky Barrier Diodes

High temperature annealing of Ni and Pt Schottky diodes on n-GaN has been investigated. Ni/n–GaN and Pt/n–GaN Schottky diodes were fabricated using ultra high vacuum and annealed at various temperatures (200 °C−700 °C) using rapid thermal anneal system. It was observed that in case of Ni/GaN diodes, the Schottky barrier height increases for 200 °C and then decreases with increase in annealing temperature. For Pt/GaN diodes, the barrier height found to decrease with increase in annealing temperature. The observed variation of barrier height and ideality factor is discussed on the basis of interfacial chemical reactions between metal and semiconductor.

Gate Leakage Current Suppression in AlGaN/GaN HEMT by RTP Annealing

Ni/Au Schottky contacts to AlGaN/GaN HEMT were formed by E-beam evaporation technique and lift-off process. The contacts were Rapid thermal annealed at 300 °C for duration of 2–10 min. A significant suppression in gate leakage current was observed at 2 and 4 min annealing. At further higher annealing duration deterioration in the reverse gate characteristics was observed.

(n)GaAs/Ti/Pt/Au Schottky contacts and their effect on MESFET's dc parameters

Abstract Rf sputtered Ti/Pt/Au Schottky contacts with varying titanium thickness have been made on (n)GaAs by the lift-off process under actual device processing conditions. The ideality factor of the Schottky barrier is dose to unity (∼ 1.07) with a barrier height of 0.80 ± 0.02 eV. The contacts with Ti films as thin as 100 A remain thermally stable with annealing up to 400°C. These contacts have been next used to fabricate submicron gate length GaAs MESFETs. The MESFETs gm increases with improved gate diode ideality but is not a strong function of it. The effect of Schottky gate annealing on the MESFETs dc characteristics shows that IDSS, gm, Vp and VR(GS) remain stable with annealing upto 350°C and degrade with 400° anneal.

Cumulative dose 60Co gamma irradiation effects on AlGaN/GaN Schottky diodes and its area dependence

Cumulative dose gamma radiation effects on current-voltage characteristics of GaN Schottky diodes have been investigated. The different area diodes have been fabricated on AlGaN/GaN high electron mobility transistor (HEMT) epi-layer structure grown over SiC substrate and irradiated with a dose up to the order of 104 Gray (Gy). Post irradiation characterization shows a shift in the turn-on voltage and improvement in reverse leakage current. Other calculated parameters include Schottky barrier height, ideality factor and reverse saturation current. Schottky barrier height has been decreased whereas reverse saturation current shows an increase in the value post irradiation with improvement in the ideality factor. Transfer length measurement (TLM) characterization shows an improvement in the contact resistance. Finally, diodes with larger area have more variation in the calculated parameters due to the induced local heating effect.

Investigation on de-trapping mechanisms related to non-monotonic kink pattern in GaN HEMT devices

This article reports an experimental approach to analyze the kink effect phenomenon which is usually observed during the GaN high electron mobility transistor (HEMT) operation. De-trapping of charge carriers is one of the prominent reasons behind the kink effect. The commonly observed non-monotonic behavior of kink pattern is analyzed under two different device operating conditions and it is found that two different de-trapping mechanisms are responsible for a particular kink behavior. These different de-trapping mechanisms are investigated through a time delay analysis which shows the presence of traps with different time constants. Further voltage sweep and temperature analysis corroborates the finding that different de-trapping mechanisms play a role in kink behavior under different device operating conditions.

Design of a 2.8 W S-band power amplifier using load pull measurement

In this work, SSPL GaN-HEMT based S-band (2.0 to 2.2 GHz) power amplifier design, fabrication, assembly and RF measurement results have been discussed. Designed single stage power amplifier is providing optimized performance over desired band with 15dB small signal gain and 2.8 W (P-1dB) CW power output with 57 % PAE. The design is based on the load pull measurement data and small signal S-parameters. Extensive load pull measurement and Co-EM simulation have been carried out for designing this circuit.

Design and development of S band 10W And 20W power amplifier

In this work, GaN-HEMT based S-band (2.7 to 3.2 GHz) power amplifier design, fabrication, assembly and RF measurement results have been presented. The Wilkinson power combiner is providing IL 0.7dB (max) and Isolation 20dB (min). Designed single stage power amplifier is providing optimized performance, over desired band with 11dB small signal gain and 10 W CW power output with 46% PAE. Using the power combining technique a power amplifier has been designed and developed which is capable to deliver 10dB small signal gain and 20W CW output power with 47% PAE in the desired band. Extensive load pull and Co-EM simulation have been carried out for designing these circuits. Cree CGH40010F device is used for design of these MIC amplifiers.

Ohmic contacts to AlGaN/GaN HEMTs: A Comparison of Two Different Ti/Al Metaletal Ratios

Ohmic contacts formed with two different metal stacks; by varying the Ti/Al thickness ratio were rapid thermal annealed in the temperature range 740–820 °C for 30 s in N2 ambience. The ohmic contact formed with Ti/Al metal thickness ratio 1/5 showed lower Rc values and smoother surface morphology compared to the contact with Ti/Al metal thickness ratio 1/1.5. The difference in behavior for both the contacts was corroborated with the outcome of different metallurgical reactions as observed by X-ray diffraction (XRD) and Energy dispersive X-ray analysis (EDX).

Effect of Ni Ions Irradiation on GaAs pHEMT Materials and Devices

GaAs/AlGaAs heterostructure based pHEMT material and fabricated pHEMT devices characteristics were studied with Ni ions irradiation at different fluences. The structural, electrical and optical characteristics were compared before and after irradiation. The structural property of the material was found unchanged while optical and electrical deterioration was observed for used fluences.