Modulation of the Bi³⁺ 6s² Lone Pair State in Perovskites for High‐Mobility p‐Type Oxide Semiconductors

Abstract

Oxide semiconductors are key materials in many technologies from flat-panel displays,solar cells to transparent electronics. However, many potential applications are hindered by the lack of high mobility p-type oxide semiconductors due to the localized O-2p derived valence band (VB) structure. In this work, the VB structure modulation is reported for perovskite Ba 2 BiMO 6 (M = Bi, Nb, Ta) via the Bi 6s 2 lone pair state to achieve p-type oxide semiconductors with high hole mobility up to 21 cm 2 V −1 s −1 , and optical bandgaps widely varying from 1.5 to 3.2 eV. Pulsed laser deposition is used to grow high quality epitaxial thin films. Synergistic combination of hard x-ray photoemission, x-ray absorption spectroscopies, and density functional theory calculations are used to gain insight into the electronic structure of Ba 2 BiMO 6 . The high mobility is attributed to the highly dispersive VB edges contributed from the strong coupling of Bi 6s with O 2p at the top of VB that lead to low hole effective masses (0.4-0.7 m e ). Large variation in bandgaps results from the change in the energy positions of unoccupied Bi 6s orbital or Nb/Ta d orbitals that form the bottom of conduction band. P-N junction diode constructed with p-type Ba 2 BiTaO 6 and n-type Nb doped SrTiO 3 exhibits high rectifying ratio of 1.3 × 10 4 at ±3 V, showing great potential in fabricating high-quality devices. This work provides deep insight into the electronic structure of Bi 3+ based perovskites and guides the development of new p-type oxide semiconductors.

Tuning of hole carrier density in p-type α-SnWO4 by exploiting oxygen defects

“…S1), indicating a p-carrier type (holes) conduction. From 0 to 30 ppm, the carrier density increased monotonically from 710 16 cm −3 to 810 18 cm −3 . The high carrier densities have been maintained one year after the initial characterization.…”

“…Quantitatively, the carrier density changes (from 710 16 cm −3 to 810 18 cm −3 ) in the range 0 to 30 ppm correspond to a change in the concentration of from 0.87 at.% to 0.86 at.% at a constant V .. O concentration of of 3.5 at.% 15 . However, in actuality, the Sn ′′ W changes in the concentration of should be less than the estimated V .. O values because the increment in the O 2 gas concentration will affect not only the amount of but also that of , as mentioned in the V .. O Sn ′′ W introductory section.…”

“…However, this disadvantage is expected to be overcome via the selection of an appropriate crystal structure based on phase stability 18 . On the other hand, the hole carrier densities of Sn 2+ -based oxide semiconductors (10 17 -10 18 cm −3 ) are several orders of magnitude greater than those of Bi 3+ -based ones (10 13 -10 14 cm −3 ) [12][13][14][15][16][17] . Such characteristics of Sn 2+ -based oxide semiconductors in terms of carrier density are useful for designing electronic devices with high conductivities.…”

“…3,[9][10][11] Recently, several p-type oxide semiconductors with ns 2 orbitals have been developed based on predictions through theoretical approaches. [12][13][14][15][16][17] These state-of-the-art p-type oxide semiconductors can be categorized into two groups: one is for Sn 2+ -based oxide semiconductors, such as pyrochlore-type Sn 2 TM 2 O 7 (TM = Nb or Ta) 13 and layered-structure SnNb 2 O 6 and a-SnWO 4 ; 14,15 and the other is for Bi 3+ -based oxide semiconductors, such as perovskite-type BaBiO 3 , 16 double-perovskite-type Ba 2 BiTMO 6 , 12,16 and pyrochlore-type Bi 2 Sn 2 O 7 . 17 Of the two, Sn 2+ -based oxide semiconductors are less chemically stable than Bi 3+ -based ones because of their metastable Sn 2+ states.…”

Bandgap-tuned barium bismuth niobate double perovskite for self-powered photodetectors with a full-spectrum response

“…Here, is used according to ref. 39. The reverse saturation current density J 0 at each temperature was extracted from the y -axis intercept at zero voltage of ln J against V (Fig.…”