Milan Kumar Bera

Low thermal budget Hf/Al/Ta ohmic contacts for InAlN/GaN-on-Si HEMTs with enhanced breakdown voltage

The authors have studied the electrical characteristics of Hf/Al/Ta ohmic contacts on In0.18Al0.82N/GaN heterostructure grown on Si (111) substrate. With annealing at 600 °C in vacuum (which is ∼200 °C lower than that for traditional Ti/Al/Ni/Au contacts), a minimum ohmic contact resistance of ∼0.58 Ω·mm and specific contact resistivity of ∼6.75 × 10−6 Ω·cm2 are obtained. The minimum contact resistance of Hf/Al/Ta contacts is comparable to that of Ti/Al/Ni/Au contacts. Owing to the lower annealing temperature, Hf/Al/Ta contacts exhibit better surface morphology and edge acuity. More importantly, Hf/Al/Ta contacts show a smooth interface with In0.18Al0.82N/GaN, whereas spike structures that penetrate the In0.18Al0.82N layer are observed for Ti/Al/Ni/Au contacts. As a result, the source–carrier-injection induced breakdown mechanism is reduced in the In0.18Al0.82N/GaN-on-Si high electron mobility transistors (HEMTs) with Hf/Al/Ta ohmic contacts, thereby leading to an improved three-terminal off-state breakdo...

Influence of PECVD deposited SiN x passivation layer thickness on In0.18Al0.82N/GaN/Si HEMT

The influence of plasma enhanced chemical vapour deposited (PECVD) silicon nitride (SiN x ) passivation film thickness on In0.18Al0.82N/GaN/Si heterostructures and HEMTs has been investigated. The formation of Si3N4 was confirmed by x-ray photoelectron spectroscopy (XPS) measurements. X-ray reflectivity (XRR) measurements reveal that both the density and roughness of the SiN x film increase with increasing film thickness. With an increase in SiN x film thickness, a significant increase in two-dimensional electron gas (2DEG) density, drain current, extrinsic transconductance and negative threshold voltage shift of the In0.18Al0.82/GaN/Si HEMTs are observed. An optimal thickness of SiN x is ~100 nm and it yields a substantial increase in 2DEG density (~30%) with a minimum sheet resistance for In0.18Al0.82N/GaN/Si heterostructures. Furthermore, we correlate the observed SiN x film thickness-dependent electrical characteristics of In0.18Al0.82/GaN/Si HEMTs with the density of the SiN x film.

Probing channel temperature profiles in AlxGa1−xN/GaN high electron mobility transistors on 200 mm diameter Si(111) by optical spectroscopy

Using micro-Raman and photoluminescence (PL) techniques, the channel temperature profile is probed in AlxGa1-xN/GaN high electron mobility transistors (HEMTs) fabricated on a 200 mm diameter Si(111) substrate. In particular, RuOx-based gate is used due to the semitransparent nature to the optical excitation wavelengths, thus allowing much accurate thermal investigations underneath the gate. To determine the channel temperature profile in devices subjected to different electrical bias voltages, the GaN band-edge PL peak shift calibration with respect to temperature is used. PL analyses show a maximum channel temperature up to 435 K underneath the gate edge between gate and drain, where the estimated thermal resistance in such a HEMT structure is about 13.7 KmmW−1 at a power dissipation of ∼10 W/mm. The temperature profiles from micro-Raman measurements are also addressed from the E2-high optical phonon peak shift of GaN, and this method also probes the temperature-induced peak shifts of optical phonon from...