T. N. Bhat

Thermally stable device isolation by inert gas heavy ion implantation in AlGaN/GaN HEMTs on Si

Multiple energies of heavy ion implantation with inert-gas ion (84Kr+) were carried out on AlGaN/GaN high-electron-mobility transistors (HEMTs) for planar device isolation. Thermal stability of the implantated samples were also investigated by isochronal annealing at 500, 600, 700, and 800 °C (each temperature for 1 h.). Due to the damages created by heavy ions (84Kr+) in the GaN lattice, the implant-isolated Al0.27Ga0.73N/GaN HEMT samples exhibited better thermal stability than 40Ar+-implant-isolation. This was also confirmed by Rutherford backscattering spectrometry in channeling condition and ultraviolet micro-Raman spectroscopy measurements. With reference to mesa-isolated AlGaN/GaN HEMTs, the buffer breakdown voltage is also stable in the implant-isolated AlGaN/GaN HEMTs. An enhanced OFF-state breakdown voltage was also realized in the implant-isolated AlGaN/GaN HEMTs. The inert gas heavy ion implantation (84Kr+) is a viable solution for the fabrication of thermally stable planar AlGaN/GaN HEMTs even...

Record-low contact resistance for InAlN/AlN/GaN high electron mobility transistors on Si with non-gold metal

We have demonstrated 0.17-µm gate-length In0.17Al0.83N/GaN high-electron-mobility transistors (HEMTs) on Si(111) substrates using a non-gold metal stack (Ta/Si/Ti/Al/Ni/Ta) with a record-low ohmic contact resistance (Rc) of 0.36 Ω mm. This contact resistance is comparable to the conventional gold-based (Ti/Al/Ni/Au) ohmic contact resistance (Rc = 0.33 Ω mm). A non-gold ohmic contact exhibited a smooth surface morphology with a root mean square surface roughness of ~2.1 nm (scan area of 5 × 5 µm2). The HEMTs exhibited a maximum drain current density of 1110 mA/mm, a maximum extrinsic transconductance of 353 mS/mm, a unity current gain cutoff frequency of 48 GHz, and a maximum oscillation frequency of 66 GHz. These devices exhibited a very small (<8%) drain current collapse for the quiescent biases (Vgs0 = −5 V, Vds0 = 10 V) with a pulse width/period of 200 ns/1 ms. These results demonstrate the feasibility of using a non-gold metal stack as a low Rc ohmic contact for the realization of high-frequency operating InAlN/AlN/GaN HEMTs on Si substrates without using recess etching and regrowth processes.

Comparison of the Al x Ga 1– x N/GaN Heterostructures Grown on Silicon-on-Insulator and Bulk-Silicon Substrates

Compared with bulk-Si wafer, AlxGa1-xN/gallium nitride (GaN) heterostructures grown on a 150-mm silicon-on-insulator (SOI) substrate with a 35-nm-thick Si overlayer are shown to have ~50% less wafer bowing. As a result, the 2-D electron gas mobility and the sheet-resistivity uniformity on SOI are improved due to a lower defect density. In terms of device performance, high-electron-mobility transistors (HEMTs) fabricated on the AlxGa1-xN/GaN-on-SOI exhibit ~20.5% higher saturation drain current as compared with the bulk-Si counterparts. However, due to the poorer conductivity of the buried oxide layer, the AlxGa1-xN/GaN-on-SOI HEMT suffers greater self-heating, with ~50 K higher channel temperature. With mitigation of self-heating, the AlxGa1-xN/GaN-on-SOI, in view of its more superior structural and thermal stability, should offer an attractive alternative for integration of the GaN technology with the Si CMOS platform.

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...