The role of boron related defects in limiting charge carrier lifetime in 4H–SiC epitaxial layers

Abstract

One of the main challenges in realizing 4H–SiC (silicon carbide)-based bipolar devices is the improvement of minority carrier lifetime in as-grown epitaxial layers. Although Z1/2 has been identified as the dominant carrier lifetime limiting defect, we report on B-related centers being another dominant source of recombination and acting as lifetime limiting defects in 4H–SiC epitaxial layers. Combining time-resolved photoluminescence (TRPL) measurement in near band edge emission and 530 nm, deep level transient spectroscopy, and minority carrier transient spectroscopy (MCTS), it was found that B related deep levels in the lower half of the bandgap are responsible for killing the minority carriers in n-type, 4H–SiC epitaxial layers when the concentration of Z1/2 is already low. The impact of these centers on the charge carrier dynamics is investigated by correlating the MCTS results with temperature-dependent TRPL decay measurements. It is shown that the influence of shallow B acceptors on the minority carrier lifetime becomes neutralized at temperatures above [Formula: see text] K. Instead, the deep B related acceptor level, known as the D-center, remains active until temperatures above [Formula: see text] K. Moreover, a correlation between the deep level concentrations, minority carrier lifetimes, and growth parameters indicates that intentional nitrogen doping hinders the formation of deep B acceptor levels. Furthermore, tuning growth parameters, including growth temperature and C/Si ratio, is shown to be crucial for improving the minority carrier lifetime in as-grown 4H–SiC epitaxial layers.

The effects of different anode manufacturing methods on deep levels in 4H-SiC p+n diodes

“…27 The level labeled B-acceptor is associated to B Si and it is known to be a common impurity in 4H-SiC epilayers, originating from the graphite parts of chemical vapor deposition reactors. 3 On the other hand, the D-center was believed to be the B Si V C complex. 28,29 However, recent density functional theory calculations have revealed that the D-center can be identified as the B C .…”

“…This, in turn, is affected by the presence of electrically active defects which behave as lifetime killers, like the carbon vacancy (V C ) and B-related defects. 2,3 The carbon vacancy (V C ) is a negative-U defect giving rise to two electrically active levels in the bandgap (E gap ) of n-type 4H-SiC, the Z 1=2 and the EH6/7 at 0.65 and 1.6 eV below the conduction band edge (E C ), respectively. 4 In particular, the Z 1=2 level is a recombination center affecting τ in bipolar devices.…”

“…4 In particular, the Z 1=2 level is a recombination center affecting τ in bipolar devices. Under certain conditions, 3 B-related centers can also act as lifetime killers. B gives rise to two levels, a shallow acceptor, found at 0.25 eV above the valence band edge (E V ) and a deeper acceptor at E V +0.50 eV.…”

“…These are related to B in a Si substitutional site (B Si ) and C-site (B C ), 5 respectively, with the former having an impact on τ for temperatures below 420 K and latter remaining active up to 570 K. 3 While the decrease of either [B Si ] or [B C ] can be achieved by acting on epigrowth parameters, e.g., a high C/Si ratio decreases (increases 3 requiring custom grown 4H-SiC epilayers, the reduction of [V C ] can be performed on any as-grown 4H-SiC epilayer. This is achieved by either oxidation 6 or diffusion of implanted C 7 or annealing (1500 C) with the use of a C-cap.…”

Boron-Related Defects in N-Type 4H-SiC Schottky Barrier Diodes

“…From the Arrhenius plots, the activation energies for hole emissions for B and D-center are estimated as E V + 0.21 and E V + 0.60 eV, respectively. They are well-known defects and have already been assigned to shallow boron (substitutional boron at the silicon site, B Si ) and deep boron (substitutional boron at the carbon site, B C ) [2,7,24,26,27].…”