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Microwave AlxGa1−xN/GaN Power HEMT's

  • Lester F. Eastman (a1)

Abstract

GaN in its hexagonal Wurtzite crystal has 3.4 eV bandgap and is capable of withstanding over 3 MV/cm electric field intensity. It is grown on either sapphire or SiC and the lattice mismatches cause threading dislocations. If it is grown along the c-axis on its Ga face, a thin pseudomorphic AlxGa1−xN barrier layer grown on top causes a substantial electrical polarization, which induces a substantial 2DEG in the GaN [1]. With x =.3 this 2 DEG is about 1 × 1013/cm2 without any doping impurities. The ∼ 109/cm2 threading dislocations accept electrons from the low density ambient donors, yielding very low net electron densities (< 1014/cm3) in the GaN buffer layer used as the HEMT channel [2]. The 2DEG electron mobility can be 1500-1700 cm2/V-s with ≥ 1 × 1013/cm2 electron sheet density. This 2DEG sheet density charge is less than the electrical polarization charge of 1.7 × 1013/cm2 for Al.3Ga.7N/GaN, due to some surface depletion and due to the fact that each dislocation traps ≥ 2 × 103 electrons. The design, processing, and measured performance of such undoped, polarization-induced HEMT's are presented below.

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[1] Ambacher, O., Foutz, B., Smart, J., Shealy, J.R., Weimann, N.G., Chu, K., Murphy, M., Sierakowski, A.J., Schaff, W.J., Eastman, L.F., Dimitrov, R., Mitchell, A., and Stutzmann, M., JAP, 87 (1) 334344 (Jan. 2000)
[2] Weimann, N.G., Eastman, L.F., Doppalapudi, D., Ny, H.M., JAP, 83, 3656 (1998)
[3] Ambacher, O., Eastman, L.F., Shealy, J.R., Smart, J., Schremer, A.T., Weimann, N.G., APL, 75 (3) (19 July 1999)
[4] Sierakowski, A.J. and Eastman, L., JAP, 86 (6), 33983401, (15 September 1999)
[5] Green, B., Chu, K., Chumbes, E., Smart, J., Shealy, J.R., and Eastman, L., IEEE Elec. Dev. Ltrs, 21 (6) 268270 (6 June 2000)
[6] Green, B., Chu, K., Smart, J., Tilak, V., Kim, H., Shealy, J.R., and Eastman, L., IEEE Microwave Guided Wave Letters, 10 (8) (August 2000)
[7] Burm, J., Schaff, W., Martin, G., Eastman, L., Amano, H., and Akasaki, I., Solid-State Electronics, 41(2) 247250 (1997)

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Microwave AlxGa1−xN/GaN Power HEMT's

  • Lester F. Eastman (a1)

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