On the Dopability of Semiconductors and Governing Material Properties

Abstract

To be practical, semiconductors need to be doped. Sometimes, they need to be doped to nearly degenerate levels, e.g., in applications such as thermoelectric, transparent electronics, or power electronics. However, many materials with finite band gaps are not dopable at all, while many others exhibit a strong preference toward allowing either p- or n-type doping but not both. In this work, we develop a model description of semiconductor dopability and formulate design principles in terms of governing material properties. Our approach, which builds upon the semiconductor defect theory applied to a suitably devised (tight-binding) model system, reveals analytic relationships between intrinsic material properties and the semiconductor dopability and elucidates the role and the insufficiency of previously suggested descriptors such as the absolute band edge positions. We validate our model against a number of classic binary semiconductors and discuss its extension to more complex chemistries and the utility in large-scale material searches.

Bandgap lowering in mixed alloys of Cs2Ag(SbxBi1−x)Br6 double perovskite thin films

“…Notably, this combination of a low-energy CBM with a highenergy VBM is expected to allow for enhanced doping and hence increased carrier concentrations in the alloy, relative to the pure materials. [48][49][50] In particular, the raised VBM, relative to pure Cs 2 AgBiBr 6 (which has been reported as intrinsically ptype), 10,16,51 should allow for greater hole carrier concentrations in the reduced-bandgap alloy. This is supported by our X-ray photoemission spectroscopy measurements, which show a reduction in the valence band to Fermi level offset when Sb is alloyed into Cs 2 AgBiBr 6 , showing the materials to become more p-type (Table S1, ESI ‡).…”

High‐Density Frenkel Defects as Origin of N‐Type Thermoelectric Performance and Low Thermal Conductivity in Mg3Sb2‐Based Materials

“…[ 3 ] However, it is not straightforward to introduce required concentration of carriers (≈10 19 –10 20 cm −3 ) in intermetallic compounds due to native charged defects, even if electronic band structures are predicted to be promising. [ 4 ]…”

“…[3] However, it is not straightforward to introduce required concentration of carriers (≈10 19 -10 20 cm −3 ) in intermetallic compounds due to native charged defects, even if electronic band structures are predicted to be promising. [4] Mg 3 Sb 2 -based Zintl compounds have attracted keen attention as a promising material for thermoelectric generators and coolers, [5][6][7][8][9][10] since the report of excellent n-type thermoelectric performance (zT ≈ 1.5 at 716 K). [11] The discovery of n-type Mg 3 Sb 2 was surprising because other numerous Zintl compounds are persistently p-type due to charged cation vacancies that pin the Fermi level near valence bands.…”

“…[12,13] The finding provided a striking example that, in intermetallic compounds, a slight deviation of nominal composition from stoichiometry notably changes a thermodynamic state and dopant stability. [4,14] To clarify how the off-stoichiometry in composition influences defect formation and electronic structures of Mg 3 Sb 2 , a variety of mechanisms were proposed using defect calculations, [11,[14][15][16] but these hypotheses lack experimental validation. Furthermore, despite having electron-crystal feature with high electron mobility, [17,18] Mg 3 Sb 2 exhibits anomalously low thermal conductivity.…”

Evaluating Materials Design Parameters of Hole-Selective Contacts for Silicon Heterojunction Solar Cells

“…Third, the material should ideally be p-type dopable, although we acknowledge notable exceptions such as MoO x : an alternate contact design approach could use a tunnel or defect recombination junction with an n-type material. Since p-type doping is trickier to assess computationally [65], only the experimentally confirmed p-type materials are considered subsequently, but one could use defect calculations to calculate dopability in a screening [66]. Fourth, as discussed previously, the VB edge energy should be aligned to within ±0.3 eV of that of a-Si:H, although the alignment does not have to be so sharp if doping is high enough.…”