Thermal stability of supersaturated MgxZn1−xO alloy films and MgxZn1−xO/ZnO heterointerfaces

Abstract

We have examined the thermal stability of wurtzite-phase Mg x Zn 1Ϫx O alloy films and ZnO/Mg x Zn 1Ϫx O bilayer films with x exceeding the reported solubility limit of 0.04. When a Mg 0.23 Zn 0.78 O film was annealed, the segregation of MgO started at 850°C and the band gap was reduced to the value of that for an xϭ0.15 film after annealing at 1000°C. Mg 0.15 Zn 0.85 O films showed no change of the band gap even after annealing at 1000°C. Therefore, we conclude that the thermodynamic solubility limit of MgO in Mg x Zn 1Ϫx O epitaxial film is about xϭ0.15. The thermal diffusion of Mg across the Mg x Zn 1Ϫx O/ZnO interface was observed only after annealing above 700°C. Unlike other II-VI semiconductors, ZnO-based alloy films and heterointerfaces are stable enough for the fabrication of high-crystallinity heterostructures.

Characterization of homoepitaxial p-type ZnO grown by molecular beam epitaxy

“…However, there is no strong evidence that Haynes' Rule even applies in ZnO, expecially for acceptors. Note that the weaker nature of the A 0 X lines in undoped SVCT ZnO is expected, because donor and acceptor concentrations in this material are about 1ϫ10 17 and 2ϫ10 15 cm Ϫ3 , respectively. 19 In comparing the undoped and N-doped samples ͑Fig.…”

“…Heterojunctions and quantum wells can also be fabricated by using MgZnO and CdZnO as the wide-gap and narrow-gap materials, respectively. [15][16][17] The homoepitaxial ZnO thin films were grown by EaglePicher Technologies, LLC ͑Miami, OK͒ in a custom-built MBE system that includes extensive cryogenic shrouding and additional cryopumping. The substrates were 10 mm ϫ10 mmϫ0.5 mm pieces cut from c-plane wafers, which themselves were sliced from bulk, 2-inch-diam ZnO ingots grown by Eagle-Picher using a seeded chemical vapor transport ͑SCVT͒ process.…”

“…The substrates were 10 mm ϫ10 mmϫ0.5 mm pieces cut from c-plane wafers, which themselves were sliced from bulk, 2-inch-diam ZnO ingots grown by Eagle-Picher using a seeded chemical vapor transport ͑SCVT͒ process. 18 Typical donor and acceptor concentrations were 1ϫ10 17 and 2ϫ10 15 cm Ϫ3 , respectively. 19 Pure ͑99.99 995%͒ Zn was supplied by means of a solidsource dual-zone effusion cell, and O and N were obtained from research-grade O 2 and N 2 , respectively, flowing through an Oxford Applied Research rf plasma source, operated at a power of 350 W. Most of the films were grown on chemomechanically polished Zn ͑0001͒ faces.…”

Multicolor Luminescence from Semiconductor Nanocrystal Composites Tunable in an Electric Field

“…3.10), while the red emission in the particles at 670 nm (E d =1.84 eV) could originate from the complex defect-related centers such as deep donor and deep acceptor centers associated with V Zn (Fig. 3.10) (Ohtomo et al, 1999;Studenikin et al, 1998b;Mitra et al, 2001). The mechanism for the formation of the excited states in the PDPV-ZnO:Mg composite structure implies the presence of channels of radiative recombination, which can be controlled by electric field.…”

Optical properties of ZnO-based quantum structures

“…We started study of ZnO epitaxial growth by using sapphire as a substrate that had large lattice-mismatch (18%) with ZnO. Our initial research results includes: (1) an observation of the excitonic laser action using grain boundaries as a cavity [3], (2) the band gap engineering based on (Zn,Mg)O and (Zn,Cd)O [4,5], and (3) optical characterizations of ZnO-based multi-quantum wells (MQWs) [6,7,8].…”