Yuvaraj Dora

ZrO2 gate dielectrics produced by ultraviolet ozone oxidation for GaN and AlGaN∕GaN transistors

We investigated the suitability of ZrO2 as a high-k dielectric for GaN material systems. Thin Zr films (4nm) were deposited by electron-beam evaporation at room temperature on n-type GaN and Al0.22Ga0.78N(29nm)∕GaN high electron mobility transistor (HEMT) structures. The Zr-coated samples were subsequently oxidized at temperatures in the range of 200–400 °C in an ozone environment. Atomic force microscopy studies after oxidation show that the ZrO2 forms a conformal layer on the underlying GaN template. Cross-section transmission electron microscopy studies showed little intermixing of the ZrO2 with the AlGaN∕GaN. The relative dielectric constant of the ZrO2 was determined to be 23. In comparison with HEMTs with bare gates (no dielectric between the gate metal and AlGaN), the HEMTs with ZrO2 showed two to three order of magnitude reduction in gate leakage current. Optimization of the HEMT process on sapphire substrates with ZrO2 under the gates yielded devices with powers of 3.8W∕mm and 58% power-added eff...

Effect of ohmic contacts on buffer leakage of GaN transistors

The effect of ohmic contacts on the buffer leakage of GaN transistors is presented. The buffer leakage for AlGaN/GaN high-electron mobility transistors and GaN MESFETs grown on the same underlying buffer was observed to be different. Controlled experiments show that the increased buffer leakage is due to the nature of the alloyed ohmic contacts and can be minimized if they are screened by the Si doping or by the two-dimensional electron gas.

High-Breakdown Enhancement-Mode AlGaN/GaN HEMTs with Integrated Slant Field-Plate

Enhancement-mode (E-mode) AlGaN/GaN high-electron mobility transistors (HEMTs) with integrated slant field-plates were developed for high breakdown voltage (VBD) and low on-resistance (RON). Combination of the self-aligned slant field-plate technology for high VBD and self-aligned CF4 plasma treatment for E-mode operation yielded high-performance device with a VBD of 1400V, which is one of the highest reported VBD value among GaN-based E-mode HEMTs. Using the active area of the device, the RON was calculated to be below 3mOmegamiddotcm2

Total GaN solution to electrical power conversion

We present the first 600V-class, total GaN solution for electrical power conversion applications. A 220V–400V boost converter using a GaN transistor and a GaN diode with fast & clean hard-switched waveforms has been demonstrated. The conversion efficiency was >99.1% at 100 kHz and >98.2% at 800 kHz.

Properties of N-polar GaN films and AlGaN/GaN heterostructures grown on (111) silicon by metal organic chemical vapor deposition

Smooth N-polar GaN films and GaN/AlGaN/GaN heterostructures with properties comparable to Ga-polar GaN-on-silicon films were grown by metal organic chemical vapor deposition on (111) silicon substrates with a misorientation angle of 3.5° toward the [112¯] direction. For heterostructures with a sheet electron density of 9×1012 cm−2 an electron mobility of 1500 cm2/V s was derived for transport parallel to the surface steps which formed as a result of the substrate misorientation.