Recombination radiation of ZnTe crystals with ap-n junction formed by the laser doping technique

Radiative recombination is studied in ZnTe-based diodes produced on the basis of a p–n junction formed by laser doping of crystals with an Al donor impurity. The luminescence spectra obtained in the case of excitation of the diodes by direct current with a density of 3 A/cm² and the photoluminescence spectra at 80 and 300 K are measured. A comparison of the photoluminescence spectra of the p-ZnTe substrate and the electroluminescence spectra at 80 K suggests that radiative recombination in the diodes occurs in the Al-doped region of the crystal. At 80 K in the electroluminescence spectra of the diodes, a band, unknown previously, with the position of the energy maximum at 2.276 eV was observed. This band can be assigned to radiative transitions between the donor level of the al atom and the valence band. For the first time, long-wave bands assigned to participation of deep, compensatory centers were not found in radiative recombination of ZnTe-based diodes. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 382–386, May–June, 1998.     

Injection of the edge electroluminescence in ZnSe MOS diodes

Injection luminescence and related properties of metal-ZnO-ZnSe-metal tunnel diodes are described. The edge emission of ZnSe is studied in the temperature range 30-300 K with respect to: a) band shape b) coupling strenght parameter, c) time resolved spectra and d) temperature dependence.External quantum efficiecies of the blue band of 2.61 × 10^-5 have been observed at 77 K. The lowest voltage threshold observed for blue band emission is 1.5 V.The relation between the electroluminescence and electrical characteristics of the MOS diodes are discussed.     

Photocurrent oscillations in luminescent epitaxial thin films of ZnSe (Cu,Ga)

Photoluminescent epitaxial thin films of ZnSe (Cu, Ga), n-type, vacuum-deposited onto CaF₂ crystals, or air cleaved mica substrates, have been studied. At temperatures between 80 K and 220 K, slow photocurrent oscillations can be observed if ZnSe (Cu, Ga) thin films are illuminated with light (200 nm ? λ ? 530 nm) and an electric field is simultaneously applied, whose value is above a definite threshold. These oscillations, with amplitude and frequency varying as a function of temperature, applied electric field and light intensity, are attributed to moving high-field domains similar to those found by Boer and co-workers on CdS single crystals. Field quenching of luminescence is observed, which visualizes moving high-field domains. Anode-adjacent high-field domains occur at applied voltages above the range at which moving domains are observed and a simultaneous electroluminescence is initiated near the anode.     

Efficient silicon light emitting diodes made by dislocation engineering

Efficient silicon-based light emitting diodes have been fabricated using the dislocation engineering method. Crucially this technique uses entirely conventional ULSI processes. The devices were fabricated by conventional low-energy boron implantation into silicon substrates followed by high-temperature annealing, and strong silicon band edge luminescence was observed. Dislocation engineering is also shown to reduce the thermal quenching for other material systems. Dislocation engineered β-FeSi₂ and Er light emitting devices were fabricated and room temperature electroluminescence at 1.5 μm was observed in both cases.     

Luminescent thin ZnS : Mn films

Photo-, cathodo-, β-luminescence spectra of the ZnS : Mn films and electroluminescence spectra of highly efficient d.c. diodes with SnO_x-ZnS : Mn-Cu_xS-ZnS : Mn-Al structure have been investigated. Strong dependence of intensity and structure of the luminescence band on applied voltage has been found. Results suggest that collision cannot be the only process causing luminescence of the d.c. diodes investigated. The yield of Mn luminescence in ZnS is found to be strongly electric field-dependent.     

可变色的ZnSe:Er3+ MIS发光二极管

本文首次利用高场和低场激发下的有效发光中心,设计和制备了随外加电压极性改变而变色的ZoSe:Er3+ MIS发光二极管。这种发光二极管在正向电压激发下得到蓝色发光,而在反向电压激发下得到绿色发光。     

Materials characterization of n - ZnO / p - GaN : Mg / c - Al2O3 UV LEDs grown by pulsed laser deposition and metal–organic chemical vapor deposition

n-ZnO/p-GaN:Mg hybrid heterojunctions grown on c-Al₂O₃ substrates showed 375 nm room temperature electroluminescence. It was suggested that the high materials and interface quality obtained using pulsed laser deposition for the n-ZnO growth and metal–organic chemical vapor deposition for the p-GaN:Mg were key factors enabling the injection of holes and the radiative near band edge recombination in the ZnO. In this paper we present the materials characterization of this structure using x-ray diffraction, scanning electron microscopy and atomic force microscopy.     

Room temperature electroluminescence from ZnO/Si heterojunction devices grown by metal-organic chemical vapor deposition

Heterojunction light-emitting diodes with ZnO/Si structure were fabricated on both high-resistivity (p) and low-resistivity (p⁺) Si substrates by metal-organic chemical vapor deposition technology. Fairly good rectifications were observed from the current-voltage curves of both heterojunctions. Ultraviolet (UV) and blue-white electroluminescence (EL) from ZnO layer were observed only from ZnO/p⁺-Si heterojunction under forward bias at room temperature (RT), while strong infrared (IR) EL emissions from Si substrates were detected from both ZnO/p-Si and ZnO/p⁺-Si heterojunctions. The UV and IR EL mechanisms have been explained by energy band structures. The realization of RT EL in UV-visible and IR region on Si substrate has great applicable potential for Si-based optoelectronic integrated circuits.     

CdS单晶中的绿色电致发光和光致发光

在50-290K温度范围内,研究了在正向电压激发下,用高纯CdS单晶制备的MIS发光二极管的电致发光光谱。在室温时,发射光谱分别由峰值为5135±25Å和5300±15Å的二个绿色谱带所组成,而在低温下,观测到有很多结构的光谱。在50K时,自由和束缚激子的发射实际上占有统治地位。文中提出,在室温时,谱峰为5135±25Å的谱带是与受导带自由电子散射的自由激子的发射有关;而谱峰为5300±15Å的谱带归结为与同时发射二个纵光学声子的自由激子的发射有关。比较了刚生长的高阻CdS单晶以及在熔融镉中热处理的低阻CdS单晶的光致发光光谱。在熔融镉中的热处理抑制了自由到束缚(HES)和束缚到束缚(LES)的边缘发射,也抑制了I2束缚激子谱线,但是增强了自由激子的发射,在电场激发下,也使自由激子的发射增强。     

Mid-infrared lasing from self-consistent quantum wells at a type II single broken-gap heterointerface

A new physical approach for the design of mid-IR lasers operating at 3–5 μm based on type II heterojunctions with effective electron–hole confinement owing to a large asymmetric band-offset at the interface (ΔE_C>0.6 eV and ΔE_V>0.35 eV) has been proposed. The creation of high barriers for carriers leads to their strong accumulation in the active region and increases the quantum emission efficiency of the spatially separated electrons and holes across the heteroboundary due to a tunnel-injection radiative recombination mechanism within the device. An extremely weak reduction of the electroluminescence (EL) intensity for the interface tunnelling-assisted emission band with increasing temperature from 77 to 300 K was observed. This coherent emission (λ=3.146 μm at 77 K) was totally polarised in the plane perpendicular to the p–n heterojunction plane, which means the laser emission was TM-polarised due to tunnelling-assisted light-hole–electron recombination across the interface.     

Enhanced electron injection in organic light-emitting devices using Al/LiF electrodes

The temperature dependence of the current-voltage-luminescence characteristics in organic light-emitting diodes (OLEDs) with varying thickness of LiF layers are studied to understand the mechanism of the enhanced electron injection by inserting a thin insulating LiF layer at the tris(8-hydroxyquinoline) aluminum (Alq₃)–Al interfaces. At room temperature, the LiF/Al cathode enhances the electron injection and the quantum efficiency (QE) of the electroluminescence (EL), implying that the LiF thin layer lowers the electron-injection barrier. However, at low temperatures it is observed that the injection-limited current dominates and the barrier height for the electron injection in the device with LiF/Al appears to be similar with the Al only device. Thus, our results suggest that at low temperatures the insertion of LiF does not cause a significant band bending of Alq₃ or reduction of the Al work function.     

Methods for spin injection managing in inGaAs/GaAs/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/CoPt spin light-emitting diodes

Spin injection in CoPt/Al₂O₃/(Al)GaAs spin light-emitting diodes (SLEDs) was studied. The oscillations of the degree of circular polarization upon variation of a distance between the active region of the SLED and a CoPt ferromagnetic injector were observed. The oscillations depend neither on a SLED material (GaAs or AlGaAs), nor on the type of injected spin-polarized carriers (electrons and holes) and are related to the action of a perpendicular magnetic field on the injected spin-polarized carriers that causes their precession. During the transfer to the active region through a distance of 50–100 nm from the injector, a z–component of a spin changes a phase that is detected experimentally as the change in sign of the degree of circular polarization of luminescence. Conceivably, a source of the internal magnetic field leading to spin precession is the magnetic field of the nonuniformly magnetized CoPt contact.     

Electroluminescence study on electron hole plasma in strained SiGe epitaxial layers

The electroluminescence (EL) of thick fully strained SiGe layers is investigated in order to clarify the recombination mechanisms. In the investigated temperature range of 20–80 K and for SiGe thickness of 70–450 nm an electron–hole plasma (EHP) is observed even at low current densities of 1 Acm⁻². In SiGe-based quantum devices the EHP condition is expected to be attained at even lower injection levels. We used the band filling model for EHP to extract the renormalized gap of SiGe in dependence on the plasma density by performing a line shape analysis of EL spectra. The results were compared with the theoretical prediction. Based on this analysis as well as on measurements and modelling of the spectral photocurrent and the external quantum efficiency, we were able to evaluate parameters of recombination transitions for EHP in SiGe. Above 200 K there is an important contribution to EL from the silicon regions. For a better evaluation of the SiGe contribution, we compared EL of SiGe diodes with EL of pure silicon diodes.     

Formation and properties of high density Si nanodots

Laser induced crystallization of ultrathin hydrogenated amorphous Si films or amorphous Si-based multilayered structures were used to get high density Si nanodots. The present technique can get size controllable Si nanodots embedded in various dielectric materials with uniform distribution which was revealed by cross-section transmission electron microscopy. Room temperature photoluminescence and electroluminescence were achieved with the emission wavelength in a visible light region both from a-SiN/Si nanodots/a-SiN sandwiched and Si nanodots/SiO₂ multilayered structures. The luminescence was associated with the radiative recombination of generated electron-hole pairs in Si nanodots or the luminescent surface states. The electroluminescence intensity is increased with increasing the injection current implying the bipolar carrier injection plays an important role in enhancing the luminescence efficiency. The formed Si nanodots by the present approach can be applied for many kinds of devices such as high efficient light emitting diodes and solar cells.     

Light-emitting silicon <Emphasis Type="Italic">pn</Emphasis> diodes

We report on the electrical and optical characteristics of silicon light-emitting pn diodes. The diodes are prepared by ion implantation of boron at high doses and subsequent high-temperature annealing. Under forward bias, the diodes emit infrared electroluminescence closely below the band gap of bulk Si. We present a rate-equation model for bound excitons, free excitons and free carriers which successfully describes the electrical and optical behaviour of the diodes at low temperatures. Especially, an electrical bistability observed below 50 K is shown to be based on the interplay of bound excitons, free excitons and free carriers in the active area of the diodes. The ionisation of bound excitons is the origin of an improved electroluminescence from the diodes at higher lattice temperatures. PACS 78.60.Fi; 78.55.Ap; 71.35.-y; 71.55.Cn     

Luminescence in x-irradiated CaF2:Co

Photoluminescence of X-irradiated CaF₂:Co single crystals is reported. The emission spectrum shows four peaks at 505, 550, 640 and 685 nm, all of them with an excitation band at 275 nm. The same emission spectrum, plus a band at 280 nm, is found in X-ray excited luminescence measurements. Thermoluminescence of 80 K X-irradiated crystals gives a glow curve with five peaks at 100, 125, 145, 190 and 225 K. The spectral distribution of these glow peaks is similar to that of the X-ray excited luminescence. The 280 nm band is associated with electron—hole recombination. The other four bands are associated with electron transitions among excited states of Co²⁺ produced by recombination of holes and Co⁺-ions created by X-irradiation.     

ZnS中Er3+的正向注入电致发光

已报导的三价稀土离子(RE3+)和二价锰离子发光的电致发光器件,都是激发机理为碰撞激发的高场发光器件[1,2]。我们研究了znS:RE2+的带边激发光谱,由此提出了实现正向注入下三价稀土离子电致发光的发光器件的设想,这种器件的必要条件是在存在三价稀土离子的区域同时注入电子和空穴。在离子注入的ZnS:Er3+发光二极管上观察到了这种发光,实验证明不是碰撞激发,而是正向注入产生的发光。     

Investigation of the effects of spin injection of charge carriers from a ferromagnetic Ni(Co)/GaAs Schottky contact in quantum well heterostructures

The circularly polarized electroluminescence of quantum-confined InGaAs/GaAs heterostructures with a ferromagnetic Ni(Co)/GaAs Schottky contact has been investigated. It is shown that the high degree of circular polarization (to 42%) is due to the injection of spin-polarized holes from the ferromagnetic metal. The dependence of the spin injection efficiency on the type of the metal/GaAs interface and the quantum well depth has been analyzed. The spin coherence length of holes was found to be ≈80 nm at 1.5 K.     

ZnSexS1-x MIS发光二极管的兰色和紫色电致发光

在40—290K温度范围内,研究了用高纯ZnSe0.8S0.2和ZnSe0.5S0.5单晶制备的MIS发光二极管在正向电压激发下的电致发光光谱。在室温时,观察到二个强的发射谱带,对于ZnSe0.8S0.2晶体,谱带峰值分别为4460和4554Å,对于ZnSe0.5S0.5晶体,则分别为4128和4276Å。在低温40K时,观察到电致发光光谱的精细结构。研究了这些光谱的温度依赖。根据作者在ZnSe MIS发光二极管中提出的观点[10],讨论了ZnSexS1-x混晶中二个室温谱带的起因。     

基于纳米硅结构的氮化硅基发光器件电致发光特性研究

利用等离子体增强化学气相沉积法制备了镶嵌于氮化硅的高密度纳米硅薄膜,并以此作为发光有源层构建基于p-Si/氮化硅基发光层/AZO结构发光二极管,在室温下观察到了电致可见发光.在此基础上,在器件p-Si空穴注入层与氮化硅基发光层之间加入纳米硅薄层作为空穴阻挡层,研究器件电致发光性质,实验结果表明器件的发光强度显著增强,并且发光效率较无纳米硅阻挡层的发光器件提高了80%以上.