ZnTe-Based Light-Emitting-Diodes Grown on ZnTe Substrates by Molecular Beam Epitaxy

Abstract

We have investigated the ZnTe-based material system for the application to light-emitting devices. To this end, ZnTe homoepitaxy techniques have been developed to grow high-quality epitaxial layers. The conductivity control of ZnTe and ZnMgSeTe layers have been investigated. High structural quality n-type ZnTe layers with high carrier concentration are achieved by aluminum doping. Ambipolar conductivity control of quaternary layers is achieved. Aluminum doped ZnMgSeTe layers show a net carrier concentration of 5 Â 10 16 cm À3 , while a high hole concentration of 2.5 Â 10 19 cm À3 is achieved by p-type doping using a nitrogen plasma source. Based on those results, Zn 1Àx Cd x Te/ZnMgSeTe triple-quantum-well(TQW) LED structures were fabricated. Bright electroluminescence was obtained at room temperature at the wavelength of 604 nm from Zn 0:7 Cd 0:3 Te and at 566 nm from Zn 0:85 Cd 0:15 Te TQW-LED.Introduction Devices emitting light at around 550 nm are strongly needed for several important applications such as medical, plastic optical fiber communication, and full color laser display applications. Although laser diodes (LDs) for violet to blue-green and red wavelength ranges are now commercially available, no succesful report on LDs in the wavelength range from the pure-green to yellow (l = 540-580 nm) have been reported yet. Moreover, the conversion efficiency of light-emitting diodes (LEDs) in this wavelength region is extremely low in comparison with that of blue and red LEDs [1].ZnTe has a direct band gap of 2.27 eV (546 nm) at room temperature, therefore it is one of the most important materials for the pure-green wavelength (l = 550 nm) region. Because of the importance of ZnTe, there have been continuous attempts to fabricate ZnTe-based LEDs. Homo-junction LEDs were fabricated by diffusion of donor impurities [2,3]. However, ZnTe-based heterojunction LEDs have not been demonstrated yet, mainly due to the problems in growing highly doped n-type epitaxial layers with high crystal quality.In this paper, molecular beam epitaxy of ZnTe-based high-quality thin films by homoepitaxy technique is reported. The conductivity control of ZnTe-based materials is investigated using aluminum and nitrogen plasma sources as a n-and p-type dopants. Heterojunction LED strutures are fabricated and current injected operation at room temperature is demonstrated.

Growth and characterization of highly nitrogen doped ZnTe films on GaAs (001) by molecular beam epitaxy

“…As a wide-gap direct bandgap II-VI compound semiconductor, ZnTe has promising prospect in the application fields of pure green light emitting diodes [1], laser diodes, terahertz emissions [2] and solar cells, such as the top cell of tandem multi-junction solar cell [3] and the intermediate-band photovoltaic solar cell [4]. It is well-known that the most of wide-bandgap II-VI compounds are unipolar semiconductors, and their doping techniques have continuously attracted many attentions in the past decades.…”

New Concept for ZnTe-Based Homoepitaxial Light-Emitting Diodes Grown by Molecular Beam Epitaxy

“…2b. In the experimentally investigated ZnCl 2 temperature range from 220 to 270 C, all ZnMgSeTe layers showed n-type conductivity and a high carrier concentration of 9.4 Â 10 17 cm --3 was observed with ZnCl 2 cell temperature of 270 C. This carrier concentration is higher than that reported up to now in n-type ZnMgSeTe films [4]. This might be caused by the insertion of nano-cluster ZnSe : Cl into Zn 0.73 Mg 0.27 Te : Cl contributing as effective donor centres.…”

“…Up to now, carrier concentrations of 4 Â 10 18 cm --3 in Al-doped n-type ZnTe [2] and of 10 17 cm --3 in Cl-doped ZnTe [3] have been reported. However, n-type ZnMgSeTe with Mg composition of 20% showed a lower carrier concentration of 5.0 Â 10 16 cm --3 caused by difficulties of doping in wide bandgap materials [4].…”

Effect of thickness on the microstructural, optoelectronic and morphological properties of electron beam evaporated ZnTe films

“…This direct bandgap nature of ZnTe with a value of 2.26 eV makes it a potential candidate for the fabrication of pure-green LED devices [3][4][5][6]. Because of its high electro-optic coefficient, ZnTe also promises to be useful in the production and detection of terahertz (THz) radiation [3,7].…”

“…Though some research groups have reported the fabrication of ZnTe based devices like LEDs and terahertz detectors, most of them have preferred highly sophisticated techniques like molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), etc. to obtain ZnTe films [3][4][5][6][7][8], electrodeposition from aqueous solutions [9,10]. ZnTe is a very attractive host for optoelectronic device realizations because of its sensitivity in the green spectral region (2.26 eV).…”