Spatial Atmospheric Atomic Layer Deposition of Al_xZn_1–xO

Abstract

The possibility of growing multicomponent oxides by spatial atmospheric atomic layer deposition has been investigated. To this end, Al(x)Zn(1-x)O films have been deposited using diethyl zinc (DEZ), trimethyl aluminum (TMA), and water as Zn, Al, and O precursors, respectively. When the metal precursors (i.e., TMA and DEZ) are coinjected in the deposition region, the Al/(Al + Zn) ratio can be accurately controlled by either varying the TMA flow to the reactor or the exposure time of the substrate to the precursors. A high doping efficiency level (up to 70%) is achieved in Al-doped ZnO, resulting in films with a high carrier density (5 × 10(20) cm(-3)), low resistivity (2 × 10(-3) Ω cm), and good optical transparency (>85%) in the visible range. The morphology of the films changes from polycrystalline, in conductive i-ZnO and Al-doped ZnO, to amorphous, in highly resistive Al-rich films. The unique combination of the fine tuning of the composition, morphology, and electrical properties of the films with high deposition rates (>0.2 nm/s) paves the way for spatial ALD as an emerging disruptive technique for the growth of multicomponent oxides over large areas.

Research Update: Atmospheric pressure spatial atomic layer deposition of ZnO thin films: Reactors, doping, and devices

“…1(c)). 5,6,16,27,31 The isolation of each gas channel is also maintained by positioning the substrate <100 nm from the gas manifold and ensuring that the exhaust flow of gases balances the inlet gas flow. 31 The substrate position may be maintained by mechanically constraining the gas manifold over the substrate, 25 floating the gas manifold over the substrate (where the gas curtains act as frictionless bearings), 32 or by floating the substrate over the gas manifold.…”

“…9,26,27,29,36,40 Nitrogen-doping of ZnO reduces its carrier concentration (thus increasing resistivity, as shown in Table II), 9,26 and it has been claimed that it can make ZnO p-type with post-deposition treatment (Table II). 26,57 The nitrogen dopant is introduced by mixing ammonia with the water oxidant precursor, and this is the method used for both conventional and spatial ALD ZnO:N. 26,58 The non-pyrophoric and low-cost nature of the ammonia precursor is in contrast to the expensive, pyrophoric organometallic materials that are often used as ALD and AP-SALD precursors, 5,14 and hence ammonia has been widely studied in both ALD and AP-SALD ZnO.…”

“…Also, the optimum Al-content leading to the lowest resistivity is often very low (e.g., 8% Al/(Al + Zn) in AP-SALD Al-doped ZnO, or AZO). 27 This means that the amount of the Al precursor pre-mixed with the Zn-metal precursor gas flow needs to be reproducibly controlled to a very low value (e.g., <10 µmol min −1 bubbling rate through the TMA precursor compared to 95 µmol min −1 through the DEZ). 27 The co-injection method is, nevertheless, successful, as can be seen from the uniform Al concentration in the XPS depth-profile shown in Fig.…”

“…We also seek to standardize the terminology used. For example, the various terms previously employed to describe these reactors are atmospheric atomic layer deposition (AALD), [23][24][25][26] spatial atmospheric atomic layer deposition (SAALD), 5,27,28 and atmospheric spatial atomic layer deposition. 29 Here, the term is standardized to AP-SALD.…”

Atmospheric Spatial Atomic Layer Deposition of In-Doped ZnO

“…[15][16][17][18] As reported in Ref. 19 the composition and electrical properties of spatial ALD ZnO:Al have been tuned accurately at high growth rates (>0.2 nm/s) by co-injecting the metal precursors. Following the same approach, ZnO:In have been grown by spatial ALD.…”