Aluminum acceptor activation and charge compensation in implanted p-type 4H-SiC

Abstract

In 4H silicon carbide, aluminum implantation causes unusual high compensation ratios as obtained from Hall effect investigations by fitting the neutrality equation with a single acceptor. We show that this approach cannot fully describe the experimental data, in particular in case of moderate doping and at high measurement temperatures above 450 K. We develop two extended models by adding an additional acceptor- or donor-like defect to the equation. Both approaches describe the data well. However, it turns out that an additional aluminum-correlated acceptor is the more reasonable choice. In this case, the compensation ratio stays almost independent of the implantation dose between 30 % and 40 %. The deep acceptor is located at EV + (280–400) meV.

Very High In‐Plane Magnetic Field Sensitivity in Ion‐Implanted 4H‐SiC PIN Diodes

“…This coincides with experimental observations of a high density of annealing persisting defects originating from aluminum implants in SiC. [44,45] Another effect is the large dependency of the observed hump and sensitivity on the overlap length of the oxide with the p+ region. The smaller the overlap, the smaller the hump and sensitivity (Figure 6).…”

“…Considering studies in literature concerning implant-induced defects, these assumptions are justified. [24][25][26][43][44][45] We note that although traps are known to be generated by both aluminum and nitrogen implants, their density can be considerably higher for aluminum implants due to the higher atomic mass of aluminum, thus creating more defects. [45] Due to their high thermal stability, implant-induced intrinsic defects can survive the high annealing temperatures, which annihilates many other extrinsic defects.…”

MD simulation study on defect evolution and doping efficiency of p-type doping of 3C-SiC by Al ion implantation with subsequent annealing

“…Although some previous studies have investigated B diffusion for p-type doping [3], a high density of boron-related deep levels [4] is generated, which degrade electrical activation. On the other hand, due to the smaller energy gap to the valence band and a strong tendency to occupy atomic sites in the silicon sublattice [5,6], and since Al does not appear an abnormal out-diffusion phenomenon as B-doped SiC during annealing [7], Al is preferred. Influenced by constraints such as doping amount and impurity atomic distribution, lowresistance p-type SiC preparation is still a difficult problem to be solved [8], because of ion implantation-induced defects which severely limit carrier lifetime and the effectiveness of doping [9].…”

Selective Doping in Silicon Carbide Power Devices

“…From the physical point of view, a limiting factor for the electrical activation of the implanted dopants is the formation of deep levels, acting as compensation centers, which occur upon irradiation and high-temperature annealing [ 37 ]. The compensating centers reduce the net-free carriers’ (electrons or holes) density in the implanted material, and this effect can be particularly pronounced in p-type-doped Al-implanted SiC layers [ 17 , 38 , 39 , 40 , 41 ]. Hence, the compensation must be taken into consideration when estimating the electrical active fraction of the implanted dopants in SiC by electrical measurements.…”