Growth and characterization of light emitting ZnS/GaN heterostructures

Abstract

Heterostructures involving ZnS/GaN show promise for the injection of holes from p-GaN into n-ZnS. Utilizing knowledge obtained from ZnS phosphor technology, this combination could result in a new type of multi-color electroluminescent display. Further, this combination provides a very interesting interface. Both ZnS and GaN are very ionic materials. Hence, it is desirable that the interface will be relatively benign, and that charge injection can occur despite the large lattice mismatch and resulting misfit defects that form near the interface. The highly lattice mismatched structures ZnS/GaN and ZnS/Al 2 O 3 were grown by molecular beam epitaxy using elemental sources. Growth rates of up to 0.4 m ph were observed for the lower growth temperatures, with rapidly diminishing rates for temperatures above 350°C. The GaN substrate consisted of a 3 m epilayer grown on sapphire ͑0001͒ by metalorganic chemical vapor deposition. Reflection high energy electron diffraction observations indicate that the zincblende ZnS layers commonly contain ͑111͒ twins, although films with no visible twin spots could be grown at a high substrate temperature. The sulfide layers were characterized using photoluminescence, x-ray diffraction, and scanning electron microscopy ͑SEM͒. X-ray peaks typically had widths of 400 arcsec for /2 scans, and somewhat worse for scans, indicating mosaic tilt. Photoluminescence spectra of the ZnS films doped with Ag and Al demonstrated the characteristic blue transition near 440 nm. SEM electron channeling patterns indicated that the ZnS films lie at a 30°rotated orientation to the Al 2 O 3 ͑0001͒ substrate, as does GaN. p-GaN/n-ZnS devices were fabricated using standard photolithography techniques. The current voltage characteristics are reported and preliminary electroluminescence results are discussed for this heterojunction system.

Electronic, vibrational, and thermodynamic properties of ZnS with zinc-blende and rocksalt structure

“…From the practical point of view, we would also like to mention that polycrystalline ZnS is available commercially as windows and domes for infrared radiation detection devices. 14 Because of its large electronic band gap, it is also useful for optoelectronic applications involving the short wavelength part of the optical spectrum 15,16 although it has recently found a strong competitor in GaN. 17 We present in this paper measurements and ab initio calculations of the specific heat C p of natural and isotopically modified zb-ZnS ( 64 Zn, 68 Zn, 32 S, 34 S) between 3 and ∼200 K (for ZnS with the natural isotope composition the work has been extended to 1100 K).…”

Deposition time and annealing effects on morphological and optical properties of ZnS thin films prepared by chemical bath deposition

“…ZnS has a large direct band gap of 3.65 eV to 3.7 eV, high refractive index of 2.25 to 2.35, and great exciton binding energy of 40 meV with n-type electrical conductivity. It has been extensively utilized in light emitting devices [2], electroluminescent devices, semiconductor lasers [3], flat panel displays [4], optical sensors [5], phosphors [6], Different techniques can be used to deposit such material in thin film form, which originate from purely physical or purely chemical processes such as close-spaced vacuum sublimation technique (CSVS) [7], molecular beam epitaxy [8], thermal evaporation [9], successive ionic layer adsorption and reaction (SILAR) [10], RF magnetron sputtering [11], chemical vapor deposition (CVD) [12], electrodeposition [13], spray pyrolysis [14] and flash evaporation technique [15]. The physical properties of the material are strongly dependent on the methods of preparation.…”

Solid phase recrystallization of ZnS thin films on sapphire

“…Details about the growth system and procedures can be found in Ref. 7. Thermal annealing at large sulfur overpressure consistently improved the structural properties of the films, thereby compensating the effects of strong mismatch.…”

“…4,5 We have recently proposed 6 and demonstrated 7 an n-ZnS:͑Ag,Al͒/ p-GaN:Mg heterostructure blue light emitting LED. The fabrication of this device requires growth of ZnS on a heavily mismatched GaN substrate.…”

“…The initial phases of growth in the heavily mismatched interface geometry are the most critical, and it is not expected that the ZnS epilayer would grow coherently for more than 1 monolayer. 7 In fact, the large mismatchrelated energy will be relaxed in the form of tilting and threedimensional relaxation. 7,8 This would certainly damage the overall crystalline quality of the ZnS layer, which is known to be critical to the performance of the II-VI-based optical devices.…”