On compensation in Si-doped AlN

Abstract

Controllable n-type doping over wide ranges of carrier concentrations in AlN, or Al-rich AlGaN, is critical to realizing next-generation applications in high-power electronics and deep UV light sources. Silicon is not a hydrogenic donor in AlN as it is in GaN; despite this, the carrier concentration should be controllable, albeit less efficiently, by increasing the donor concentration during growth. At low doping levels, an increase in the Si content leads to a commensurate increase in free electrons. Problematically, this trend does not persist to higher doping levels. In fact, a further increase in the Si concentration leads to a decrease in free electron concentration; this is commonly referred to as the compensation knee. While the nature of this decrease has been attributed to a variety of compensating defects, the mechanism and identity of the predominant defects associated with the knee have not been conclusively determined. Density functional theory calculations using hybrid exchange-correlation functionals have identified VAl+nSiAl complexes as central to mechanistically understanding compensation in the high Si limit in AlN, while secondary impurities and vacancies tend to dominate compensation in the low Si limit. The formation energies and optical signatures of these defects in AlN are calculated and utilized in a grand canonical charge balance solver to identify carrier concentrations as a function of Si content. The results were found to qualitatively reproduce the experimentally observed compensation knee. Furthermore, these calculations predict a shift in the optical emissions present in the high and low doping limits, which is confirmed with detailed photoluminescence measurements.

Probing structural and chemical evolution in (AlxGa1−x)2O3using atom probe tomography: A review

“…A DX transition center occurs when a donor impurity captures two electrons and undergoes a large lattice relaxation to transform into an acceptor, resulting in fewer electrons available for conduction. Another factor that is accounted for compensating knee is the material defects [99].…”

“…In this case, considering Si as the atom of interest (atom i), the concentration profile of Al and Ga (atom j) starting from each Si atoms in a radially outward direction within small volumes was measured via RDF as illustrated in Fig. 14 [99]. The information obtained from this analysis was significant in understanding which kind of cationic site n-type dopants would occupy and the type of dominant defects that would be responsible for dopant compensation in (Al x Ga 1−x ) 2 O 3 when Al content is varied.…”

Survey of acceptor dopants in SrTiO3: Factors limiting room temperature hole concentration

“…This work aims to fill this gap in the literature and discuss factors limiting and potential pathways to enhance p ‐type conductivity in SrTiO 3 by performing a computational survey of several dopants conventionally thought of as acceptors. This is done using a grand canonical defect model informed by defect formation energies derived from hybrid exchange‐correlation density functional theory (DFT) calculations–a procedure widely used in research on charged point defects in other wide bandgap semiconducting materials such as the III‐nitrides . Formation energies for native defects and extrinsic defects from Al, Cu, Fe, K, Mg, Mn, N, Na, Ni, and Zn are presented as a function of Fermi level ( μ e ) in various processing conditions.…”

“…This is done using a grand canonical defect model informed by defect formation energies derived from hybrid exchange-correlation density functional theory (DFT) calculations-a procedure widely used in research on charged point defects in other wide bandgap semiconducting materials such as the III-nitrides. [44][45][46][47] Formation energies for native defects and extrinsic defects from Al, Cu, Fe, K, Mg, Mn, N, Na, Ni, and Zn are presented as a function of Fermi level (μ e ) in various processing conditions. Tracking and using the many first-principles simulations required to properly treat these impurities was facilitated by using a point defect informatics framework.…”

Optimizing n -type doping of ZnGeN2 and ZnSiN2

“…For example, Si Ga acts as a shallow donor in GaN, but for Al x Ga 1−x N with high Al concentration, silicon has a transition level between the positive and negative charge states that lies within the band gap [16]. As a result, it is difficult to achieve high carrier concentrations in Al x Ga 1−x N [17]. With a different set of potential donors, the Zn-IV-nitrides could potentially enable levels of n-type doping that are difficult to achieve in…”