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(a) Simulated band diagram of regrown InN source-drain regions for a N-polar GaN HEMT. The high at the InN and GaN interface is a barrier to the flow of electrons from the metal to the 2DEG. (b) Simulated band diagram of InGaN graded from for source-drain regions of a N-polar GaN HEMT.
[(a)–(e)] Top view scanning electron micrographs of InN source-drain regions regrown at growth temperatures of (a) , (b) , (c) , and (d) . (e) Cross-sectional SEM image of regrown InN source-drain region next to the gate stripe, which shows minimal shadowing effect near the gate. Polycrystalline InN growth is observed on top of the gate stripe. [(f)–(h)] Top view scanning electron micrographs of regrown graded InGaN layers grown at (f) , (g) , and (h) .
(inset) Epitaxial structure of the samples with 40 nm InGaN graded from 1% to A (30%), B (54%), and C (63%) and 10 nm InN cap. HRXRD for sample C with peaks corresponding to regrown InN and graded InGaN indicated.
(a) Ohmic Contact resistance (open circles) values for graded InGaN grown at varying growth temperature (Table I). Variation in Ohmic contact resistance with final composition of graded InGaN (samples A, B, and C) with an InN cap (filled squares) (b) TLM measurements of sample C from which an Ohmic contact resistance of was extracted by linear fit (red line). (Inset: top view SEM scan of sample C which shows InN islands and a smooth regrown InGaN source drain region.)
I-V characteristics of a self aligned regrown Ohmic contact N-polar HEMT, with gate .
(a) Final InGaN composition in the grade obtained by varying the growth temperature, and keeping the end Ga-flux constant. (b) Second grading scheme in which the growth temperature was kept constant but the final Ga-flux was decreased to obtain higher In incorporation and steeper grading profile.
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