Tailoring the Hole Mobility in SnO Films by Modulating the Growth Thermodynamics and Kinetics

Abstract

Obtaining semiconducting properties that meet practical standards for p-type transparent oxide semiconductors is challenging due to the balance between the defects that generate hole and electron carriers. Here, we demonstrate that modulating the individual thermodynamic and kinetic conditions during the growth of p-type oxide SnO films is beneficial in tailoring their semiconducting properties. By tuning the growth temperature and laser fluence for pulsed laser deposition, the hole carrier density dramatically changes from approximately 4 × 10 16 to 6 × 10 18 cm −3 at room temperature. The room-temperature hole mobility (μ) strongly depends on the carrier density (n), and their relationship is like a "volcano-shaped" curve. This suggests the competition between several scattering sources, such as the ionized impurity scattering (μ ∝ n −1 ), and grain boundary and/or dislocation scattering (μ ∝ n 0.5 ) for higher and lower n, respectively. The hole mobility is enhanced to approximately 21 cm 2 V −1 s −1 at room temperature, which is the highest recorded for SnO films to date. These findings provide important guidelines for designing all-oxide transparent electronic devices.

Development of a high-precision XYZ translator and estimation of beam profile of the vacuum ultraviolet and soft X-ray undulator beamline BL-13B at the Photon Factory

“…The ES width and photon energy are set to 30 mm and material for practical devices as a p-type oxide semiconductor. Recently, we improved the hole mobility of an SnO film by modulating the growth thermodynamics and kinetics (Minohara et al, 2019(Minohara et al, , 2020. Fig.…”

Plasma-assisted molecular beam epitaxy of SnO(001) films: Metastability, hole transport properties, Seebeck coefficient, and effective hole mass

“…Common challenges for the growth of phase-pure SnO are its metastability with respect to the disproportionation into SnO 2 and Sn, as well as the adjustment of the stoichiometry to prevent the formation of secondary SnO 2 or Sn phases. Note that despite the non-equilibrium nature of thin film growth, equilibrium phase diagrams can provide guidance as discussed next: Firstly, the stability region of SnO at temperatures between 197 and 410 • C (and disproportionation outside this region) rationalizes why most SnO films have been obtained at growth or annealing temperatures in this temperature range; [7][8][9]12,17,20 secondly, during growth by reactive sputtering 9,13 , PLD, 10,18 or MBE 19 the formation of secondary SnO 2 or Sn-phases has been controlled by adjusting the stoichiometry of the source vapor, i.e., the oxygen (background) pressure at fixed flux of SnO x from the source, in qualitative agreement with the equilibrium stoichiometry dependence in the phase diagram. The blue or orange shaded regions as well as colored arrows in Fig.…”

“…5 In fact, hole mobilities between 1 and 5 cm 2 Vs have typically been obtained by Hall measurements of SnO films. 5,[7][8][9][10] More recently, hole mobilities as high as 30, 21, and 19 cm 2 Vs have been reported for polycrystalline SnO bulk ceramics, 11 optimized epitaxial SnO(001) layers, 12 and polycrystalline, mixed SnO+Sn films, 13 respectively. Thus, reasonably high hole mobilities together with a direct bandgap absorption edge arXiv:2007.13448v2 [cond-mat.mtrl-sci] 3 Aug 2020 around 2.6-3.2 eV (and only weak optical absorption by its indirect band gap of 0.6 eV), 5,7,8 fuel the interest in SnO as a p-type semiconducting oxide for transparent thin film transistor applications.…”

“…10 The observed p-type conductivity of unintentionally doped (UID) SnO has been correlated by first-principle calculations with Sn vacancies 14 or their complexes with hydrogen 15 acting as shallow acceptors, whereas oxygen interstitials were predicted to be electrically inactive. 14,15 SnO thin films have been grown by various methods, such as electron-beam evaporation 16 or reactive DC magnetron sputtering, 13 both followed by thermal annealing, reactive ion beam sputter deposition, 9 pulsed laser deposition (PLD) from an oxide target 10,12,17 or a metallic Sn target 18 , and molecular beam epitaxy (MBE). 8,19,20 The largest challenge for the growth of phase pure SnO is its metastability with respect to its stable relatives Sn and SnO 2 .…”

Site-Selective Oxygen Vacancy Formation Derived from the Characteristic Crystal Structures of Sn–Nb Complex Oxides

“…Thus, oxides including cations with ns 2 electronic configuration (such as Sn 2+ , Pb 2+ , and Bi 3+ ) have attracted attention as new candidates for p-type oxides [3][4][5][6][7]. This approach was demonstrated through the fabrication of SnO films with a hole mobility of ~21 cm 2 V -1 s -1 [8][9][10][11]. However, because SnO has an indirect band gap of 0.7 eV [9], it is not suitable for future transparent device applications.…”