University of California

University of Notre Dame Du Lac

Huili Xing

Debdeep Jena

Umesh Kumar Mishra

John David Simon

Siddharth Rajan

A compositionally graded semiconductor device and a method of making same are disclosed that provides an efficient p-type doping for wide bandgap semiconductors by exploiting electronic polarization within the crystalline lattice. The compositional graded semiconductor graded device includes a graded heterojunction interface that exhibits a 3D bound polarization-induced sheet charge that spreads in accordance with &#x3c1;(z)=&#x2212;&#x2207;&#xb7;P(z), where &#x3c1;(z) is a volume charge density in a polar (z) direction, and &#x2207; is a divergence operator, wherein the graded heterojunction interface is configured to exhibit substantially equivalent conductivities along both lateral and vertical directions relative to the graded heterojunction interface.

Compositionally graded heterojunction semiconductor device and method of making same

Novel GaN/AlGaN metal-semiconductor field-effect transistor (MESFET) structures grown without any impurity doping in the channel. A high-mobility polarization-induced bulk channel charge is created by grading the channel region linearly from GaN to AlGaN over a distance, e.g., 1000 &#x212b;. A polarization-doped field effect transistor (PolFET) was fabricated and tested under DC and RF conditions. A current density of 850 mA/mm and transconductance of 93 mS/mm was observed under DC conditions. Small-signal characterization of 0.7 &#x3bc;m gate length devices had a cutoff frequency, f=19 GHz, and a maximum oscillation of f=46 GHz. The PolFETs perform better than comparable MESFETs with impurity-doped channels, and are suitable for high microwave power applications. An important advantage of these devices over AlGaN/GaN HEMTs is that the transconductance vs. gate voltage profile can be tailored by compositional grading for better large-signal linearity.

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Huili Xing