Zinc Oxide Grown by Atomic Layer Deposition: From Heavily n‐Type to p‐Type Material

Abstract

ZnO grown by atomic layer deposition (ALD) is an interesting material for electronic applications requiring low processing temperature. Herein, it is shown that the electrical conductivity of ZnO ALD films can be varied from 10 À1 to 10 2 Ω À1 cm À1 by moving the growth conditions from oxygen rich to zinc rich, through changing the deposition temperature between 100 and 200 C. The temperature-dependent photoluminescence (PL) studies show evidence that shallow defect states in ZnO ALD films are clearly influenced by oxygen-and zincrich conditions, which affect the binding energy of existing donors as well as the relative intensity from donor-to acceptor-related luminescence. The films grown at 100 C, under O-rich conditions, are more resistive and show considerably more intensive acceptor-related PL bands than those grown at 200 C, when Znrich conditions are achieved. Moreover, scaling of electron concentration with the growth temperature is accompanied by a variance of the bandgap due to the Burstein-Moss effect. It is shown that the acceptor-related conductivity of ZnO ALD can be achieved by nitrogen doping under O-rich conditions. The related homojunction with the rectification ratio of 4 Â 10 4 (at AE 2 V) is obtained based on ZnO ALD films deposited at 100 C.

Hydrogen in As‐Grown and Annealed ZnO Films Grown by Atomic Layer Deposition

“…In detail, the reported hydrogen concentration varies www.advancedsciencenews.com www.pss-a.com from %10 20 to %10 21 at cm À3 in as-grown ZnO films and can be reduced to %10 19 at cm À3 after 3 min of annealing at 800 C. [21] SIMS profiles measured in the present study reveal that the average hydrogen content in the as-grown ZnO samples of the H series varies bewteen %2.5 Â 10 20 and %1.1 Â 10 21 at cm À3 (with the hydrogen profile in the H100 sample shown in Figure 2a) and decreases with increasing growth temperature, as previously reported. [21,31,32] The same trend is observed in the D series for both hydrogen and deuterium, thus indicating that hydrogen residuals originating from both the unreacted metalorganic ligands and -OH groups actually decrease with increasing T g . Furthermore, in this case, the hydrogen concentration is found to be lower, between %5.7 Â 10 19 and %3.5 Â 10 20 at cm À3 , in agreement with DEZn being the only source of hydrogen contamination into the films (see also Figure 2b).…”

“…Growth processes lasted 1500 ALD cycles with an expected ZnO layer's thickness between %220 and 270 nm according to the deposition rates in the ALD growth window. [31,38] The ALD growth parameters were chosen as for ZnO films optimized for high conductivity, [39] i.e., pulsing/purging times were set equal to 40 ms/8 s and 16 ms/22 s for DEZn and water precursors, respectively. www.advancedsciencenews.com www.pss-a.com…”

Structural Properties of Thin ZnO Films Deposited by ALD under O-Rich and Zn-Rich Growth Conditions and Their Relationship with Electrical Parameters

“…It should be noted that the ZnO films were deposited on both substrates together during the same ALD process. The series of samples were obtained at temperatures, T g , of 100, 130, 160, 200, 250, and 300 • C. It was shown that, in this T g range, the stoichiometry of the deposited ZnO films changes from O-rich (at 100 • C) to Zn-rich (at 200 • C and above) [6,18]. The thickness of the ZnO/Si layers (100-150 nm) was measured with a reflectometer using a NanoCalc 2000 (Mikropack GmbH, Ostfildern, Germany), and the thickness of the ZnO/a-Al 2 O 3 films (100 nm) was measured with a profilometer (Dektak 6M stylus, Veeco, Tucson, AZ, USA).…”

“…However, recent investigations strongly suggest that hydrogen impurity in ZnO material may be involved in a number of complexes with native point defects, such as V Zn •nH, Zn i •V O •H, and others [2][3][4][5][11][12][13][14]. Some of these complexes introduce shallow donor and acceptor levels that affect the resulting ZnO conductivity [4,10,[15][16][17][18].…”

Defects in complex oxide thin films for electronics and energy applications: challenges and opportunities

“…305,306 Despite its intrinsic advantages, the lack of control over dopants and defects hindered its further application to practical devices, thus stimulated a boom over investigating the defect chemistry in ZnO. 302,[307][308][309][310] The as-grown ZnO crystals normally exhibit n-type conductivity, which was initially attributed to the native defects such as Zn interstitials, Zn vacancies or V O (Fig. 12a).…”