Robert Laishram

Passivation of AlGaN/GaN HEMT by Silicon Nitride

We report here the passivation of AlGaN/GaN HEMT devices with silicon nitride films deposited by inductively coupled plasma chemical vapour deposition (ICPCVD). With low power ammonia plasma pretreatment and silicon nitride film passivation having refractive index of 2.01 and 2,000 A0 thickness, 80–95 % current recovery and minimum knee walkout have been achieved on different samples.

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.

Silicon nitride films for passivation of pHEMT based MMIC

Passivation of psuedomorphic high electron mobility transistor (pHEMT) based MMICs by silicon nitride films deposited by PECVD is reported here. These films were first optimized for passivation of MESFETs to get desired performance. No degradation in pHEMT/MESFET characteristics like Idss, gm Vp and Cgs were observed while only nominal degradation was found in Schottky diode ideality factor eta and its breakdown voltage VB. The refractive index of the films was 1.92 with 1200 A0 thickness. The films have high dielectric strength > 5E6 V/cm, low tensile stress < 5E9 dynes/cm2 and dielectric constant 6.9 -7.1. The etch rate of the film is ~ 900 A0/min in BHF and fine patterns can be etched with 1-2 minutes etch time in BHF. The film composition was analyzed by FTIR and SIMS studies.

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.

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).