High-Field Transport and Impact Ionization in Wide Bandgap Semiconductors

Self Cite

Impact ionization plays a crucial role for electron transport in semiconductors at high electric fields. We derive appropriate quantum kinetic equations for electron transport in semiconductors within linear response theory. The field-dependent collision integral is evaluated for the process of impact ionization. A known, essentially analytical result is reproduced within the parabolic band approximation ͓W. Quade et al., Phys. Rev. B 50, 7398 ͑1994͔͒. Based on the numerical results for zero field strengths but realistic band structures, a fit formula is proposed for the respective field-dependent impact ionization rate. Explicit results are given for GaAs, Si, GaN, ZnS, and SrS.

Section: Introductionmentioning

confidence: 99%

Field effect on the impact ionization rate in semiconductors

Redmer

Madureira

Fitzer

et al. 2000

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“…The wave vector dependent, electron initiated impact ionization rates have been calculated for the wide band gap materials ZnS, 4-6 GaN, 7,17 and SrS according to Eq. ͑1͒ using the EPM band structures given in Fig.…”

Section: Results For the Impact Ionization Ratementioning

confidence: 99%

“…7 The respective energy dependent impact ionization rates have already been used in full-band Monte Carlo simulations of high-field electron transport. [5][6][7] Based on that microscopic approach, we present new results for the hole initiated impact ionization rates for the cubic wide band gap materials ZnS, GaN, and SrS, which show a very different behavior than the electron rates. These new results are important for the interpretation of the measured impact ionization coefficient.…”

Section: Introductionmentioning

confidence: 99%

Hole initiated impact ionization in wide band gap semiconductors

Reigrotzki

Redmer

Fitzer

et al. 1999

Band-to-band impact ionization by hot electrons and holes is an important process in high-field transport in semiconductors, leading to carrier multiplication and avalanche breakdown. Here we perform first principles calculations for the respective microscopic scattering rates of both electrons and holes in various wide band gap semiconductors. The impact ionization rates themselves are calculated directly from the electronic band structure derived from empirical pseudopotential calculations for cubic GaN, ZnS, and SrS. In comparison with the electron rates, a cutoff in the hole rate is found due to the relatively narrow valence bandwidths in these wide band gap semiconductors, which correspondingly reduces hole initiated carrier multiplication.

“…Previous calculations for Si and GaAs, 3,4 ZnS, [5][6][7] SrS, 8 GaN, [8][9][10][11] InN, 12 and SiC, 13 again neglecting the field influence during the collision, have shown that the entire band structure in the Brillouin zone has to be considered when numerically evaluating the corresponding matrix element including direct, exchange, and umklapp processes. Pronounced contributions arise from higher conduction bands, especially in wide band gap materials like ZnS, GaN, or SrS.…”

Section: Introductionmentioning

confidence: 99%

Impact ionization rates of semiconductors in an electric field: The effect of collisional broadening

Madureira

Semkat

Bönitz

et al. 2001

Calculation of the electron initiated impact ionization transition rate in cubic and hexagonal phase ZnSA gauge invariant quantum kinetic equation which includes impact ionization, intracollisional field effect, and collisional broadening is derived in the frame of nonequilibrium Green's functions. We obtain analytical expressions for the impact ionization rate. For the wide band gap material ZnS, a substantial increase of the rate due to collisional broadening is obtained for moderate field strengths Eр500 kV/cm.