Density and energy level of a deep-level Mg acceptor in 4H-SiC

Abstract

Reliably determining the densities and energy levels of deep-level dominant acceptors in heavily doped wide-band-gap semiconductors has been a topic of recent discussion. In these discussions, the focus is on both Hall scattering factors for holes and distribution functions for acceptors. Mg acceptor levels in 4H-SiC seem to be deep, and so here the electrical properties of Mg-implanted 4H-SiC layers are studied by measuring Hall effects. The obtained Hall scattering factors are not reliable because they drop to less than 0.5 at high measurement temperatures. Moreover, the Fermi–Dirac distribution function is unsuitable for examining Mg acceptors because the obtained acceptor density is much higher than the concentration of implanted Mg atoms. However, by using a distribution function that includes the influence of the excited states of a deep-level acceptor, the density and energy level of Mg acceptors can be reliably determined.

Relationship between Temperature Dependencies of Resistivity and Hall Coefficient in Heavily Al-Doped 4H-SiC Epilayers

“…The resistivity in the band conduction region (ρBand(T)) can be expressed as ρBand(T) = 1/qp(T)μBand(T), where q is the elementary charge, p(T) is the temperature-dependent hole concentration in the valence band, and μBand(T) is the temperature-dependent hole mobility in the valence band. Because p(T) is proportional to exp(-ΔEA/kBT) in heavily Al-doped 4H-SiC [8,13] and varies with T much more sharply compared with μBand(T), ΔEρBand becomes close to ΔEA, where ΔEA is the activation energy, which is usually between (EAl -EV)/2 and (EAl -EV) [14]. Here, kB is the Boltzmann constant, EAl is the Al acceptor level, and EV is the top of the valence band.…”

“…Previous studies reported on the conduction mechanisms in n-type 4H-SiC with a N concentration on the order of 10 18 cm -3 [5] and p-type 6H-SiC with an Al concentration (CAl) below 1.6 × 10 19 cm -3 [6,7]. To obtain p-type 4H-SiC with very low resistivity, Al acceptors are selected rather than Be, B, or Mg acceptors because Al acceptors have the lowest acceptor level [8]. For the 6H-SiC wafer with CAl of 1.6 × 10 19 cm -3 [6], the Hall coefficient (RH) had a maximum at approximately 160 K, which is close to the temperature (TBH) at which the dominant conduction mechanism changes from band conduction to hopping conduction, and RH decreased as the temperature was decreased further.…”

Comparison of Conduction Mechanisms in Heavily Al-Doped 4H-SiC and Heavily Al- and N-Codoped 4H-SiC

“…In particular, it is essential to develop fabrication methods for p-type SiC layers or wafers with a much lower resistivity than that currently achievable [3,4] Previous studies have reported on the conduction mechanisms in n-type 4H-SiC with a N concentration (C N ) on the order of 1×10 18 cm −3 [5] and p-type 6H-SiC with an Al concentration (C Al ) below 1.6×10 19 cm −3 [6,7]. To obtain p-type 4H-SiC with very low resistivity, we selected Al acceptors rather than Be, B, or Mg acceptors because Al has the lowest acceptor level [8]. To reduce the resistivity in heavily doped p-type 4H-SiC, it is necessary to understand the conduction mechanisms in heavily Al-doped 4H-SiC epilayers or wafers with C Al values higher than 1×10 19 cm −3 .…”