Publication Date:
2014-09-09
Description:
Oxide/semiconductor interface trap density ( D it ) and net charge of Al 2 O 3 /(GaN)/AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistor (MOS-HEMT) structures with and without GaN cap were comparatively analyzed using comprehensive capacitance measurements and simulations. D it distribution was determined in full band gap of the barrier using combination of three complementary capacitance techniques. A remarkably higher D it (∼5–8 × 10 12 eV −1 cm −2 ) was found at trap energies ranging from E C -0.5 to 1 eV for structure with GaN cap compared to that ( D it ∼ 2–3 × 10 12 eV −1 cm −2 ) where the GaN cap was selectively etched away. D it distributions were then used for simulation of capacitance-voltage characteristics. A good agreement between experimental and simulated capacitance-voltage characteristics affected by interface traps suggests (i) that very high D it (〉10 13 eV −1 cm −2 ) close to the barrier conduction band edge hampers accumulation of free electron in the barrier layer and (ii) the higher D it centered about E C -0.6 eV can solely account for the increased C-V hysteresis observed for MOS-HEMT structure with GaN cap. Analysis of the threshold voltage dependence on Al 2 O 3 thickness for both MOS-HEMT structures suggests that (i) positive charge, which compensates the surface polarization, is not necessarily formed during the growth of III-N heterostructure, and (ii) its density is similar to the total surface polarization charge of the GaN/AlGaN barrier, rather than surface polarization of the top GaN layer only. Some constraints for the positive surface compensating charge are discussed.
Print ISSN:
0021-8979
Electronic ISSN:
1089-7550
Topics:
Physics
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