P-Type ZnO:P Films Fabricated by Atomic Layer Deposition and Thermal Processing

Abstract

P-type phosphorus-doped ZnO (ZnO:P) films were fabricated by atomic layer deposition of ZnO upon the amorphous silica substrates, which were prepared by coating the spin-on dopant consisted of P 2 O 5 and SiO 2 on silicon wafers. Post-deposition thermal treatments were carried out to diffuse the phosphorus dopants into ZnO and to activate the phosphorus-related acceptor states. The ZnO:P films exhibited p-type conductivity with an average hole concentration of 1.05 Â 10 17 cm À3 . Significant spectral peaks associated with the acceptor states appeared in the low-temperature photoluminescence spectra of the p-type ZnO:P films. Optically-pumped stimulated emission around 393 nm was observed at room temperature, thereby indicating a good optical quality of the p-type ZnO:P film.Zinc oxide (ZnO) is a promising material for ultraviolet (UV) light-emitting diodes (LEDs) and laser diodes because of its direct band gap ($3.37 eV) and large excitonic binding energy up to 60 meV. 1-12 ZnO also has many benefits, for instance, compatibility with conventional wet chemical etching, low material cost, long-term stability, low environmental impact, and excellent radiation resistance. Several papers have reported the preparation of high-quality ZnO films using molecular beam epitaxy (MBE), 1-3 metal-organic chemical vapor deposition, 4,5 hybrid beam deposition, 6 chemical vapor deposition, 7,8 pulsed laser deposition (PLD), 9,10 and filtered cathodic vacuum arc technique. 11,12 Atomic layer deposition (ALD) is an alternative and potential technique to grow high-quality ZnO films. 13-15 It is a surface-controlled process of depositing materials with atomic-layer accuracy. Each precursor is alternately introduced into the chamber and the chemical reactions proceed at the substrate surface, leading to self-limiting and layer-by-layer growth. Hence ALD has many advantages over other techniques, including easy and accurate thickness control, conformal step coverage, high uniformity over a large area, low defect density, low deposition temperatures, and good reproducibility. 13,14 High-quality n-type ZnO films grown by ALD on c-sapphire substrates and treated by post-deposition annealing were demonstrated in our previous study. 16 The threshold intensity of stimulated emission in the n-ZnO films was as low as 35.1 kW/cm 2 , primarily ascribed to the high crystalline of the ZnO films grown by ALD.Although ZnO has a drawback of difficulty in preparing highquality and reliable p-type films, several groups have reported the growth of p-type phosphorus-doped ZnO (ZnO:P) films using MBE, 17 PLD,18, In our understanding, there is still no report on the p-type ZnO films grown upon amorphous substrates, since the well-crystallized films could not be expected because of the lack of epitaxy of ZnO on amorphous substrates. Recently, we have demonstrated highly c-axis oriented ZnO films, accompanied by the onset of optically-pumped stimulated emission, grown on amorphous glass substrates by the ALD technique. 21 In the present paper, we demonstrat...

Atomic layer deposition of ZnO: a review

“…This has been notoriously difficult for ZnO due to the high level of carrier doping from intrinsic defects. Nonetheless, both nitrogen and phosphorus doping were successfully used to turn ZnO's conductivity into p-type [107][108][109][110][111][112], although in all cases a post-annealing procedure was necessary to remove the n-type carrier doping from defects and donor impurities in ZnO. In the case of N-doped ZnO films, the typically used dopant is NH 3 , which is proposed to occupy an O site in the ZnO structure with NH [107,108].…”

Atomic Layer Deposition of p‐Type Semiconducting Thin Films: a Review

“…This has however been notoriously difficult for ZnO because of the high level of intrinsic carrier doping from oxygen vacancies and zinc interstitial defects. Nonetheless, both nitrogen and phosphorus were successfully incorporated to turn ALD ZnO films into p-type, [182,184,185,[238][239][240] albeit a post-deposition annealing was required to remove the n-type carrier doping from defects and donor impurities. The major drawback for the fabrication of homodiodes is the higher resistivity of the p-type ZnO films compared to n-type ZnO films.…”

Ultraviolet Electroluminescence from Nitrogen-Doped ZnO-Based Heterojuntion Light-Emitting Diodes Prepared by Remote Plasma in situ Atomic Layer-Doping Technique

“…Subsequently, the ZnO:N/GaN:Mg structure was treated by rapid thermal annealing (RTA) at 1000 °C in oxygen atmosphere for 5 min to improve the crystalline quality as well as the uniformity of dopant distribution in the ZnO:N layer. Since oxygen vacancies in ZnO were considered as the donors in ZnO, 17 the oxygen atmosphere in the post-RTA treatment was used to reduce the density of oxygen vacancies. Afterward, a circular ZnO:N mesa of 1 mm in diameter was fabricated via the conventional lithography and the wet chemical etching by a very dilute HCl solution.…”