On the thermal and optical properties of ZnSe and doped ZnSe crystals grown by PVT

Single crystals of ZnSe, phosphorus-doped ZnSe and phosphorus with Gallium-doped ZnSe have been grown by physical vapour transport technique. The thermal properties like thermal diffusivity, effusivity and conductivity are studied using photoacoustic spectroscopy and differential scanning calorimetry, for the use of substrate. Their optical properties are also studied using Raman, photoluminescence and photocurrent for the study of the site symmetry of the phosphorus. Our measurements reveal the possibility of phosphorus going to deep level thus reducing to C_3v level.     

Growth and annealing effect of high-quality ZnSe:N/ZnSe by MOCVD

The ZnSe : N epitaxial layers were grown on (1 1 0) ZnSe substrates in a low-pressure metalorganic chemical vapor deposition (MOCVD) system using hydrogen as a carrier gas, and using ammonia as a dopant source. In order to obtain highly doped ZnSe : N epitaxial layers, the optimum growth and doping conditions were determined by studying the photoluminescence (PL) spectra from the ZnSe epitaxial layers grown at different ammonia flux and VI/II flux ratio. Furthermore, in order to enhance the concentration of active nitrogen in ZnSe epitaxial layer, a rapid thermal anneal technique was used for post-heat-treating. The results show that the annealing temperature of over 1023 K is necessary. Beside, a novel treatment method to obtain a smooth substrate surface for growing high quality ZnSe epitaxial layers is also described.     

Influence of Annealing in Zinc Vapor on the Microstructure and Activator Radiation of ZnSe : Fe

Crystallography Reports - The effect of thermal treatment in zinc vapor on the stoichiometry, defect and impurity structure, and activator cathodoluminescence of ZnSe doped with iron by the thermal...     

双温区热扩散掺杂Fe2+∶ZnSe激光晶体的制备及激光输出性能

本文以CVD ZnSe晶片为基质材料,以FeSe粉末为掺杂物,采用双温区热扩散掺杂技术获得了尺寸为Ø22 mm×4 mm的Fe²⁺∶ZnSe激光晶体。通过二次离子质谱(SIMS)测试该晶体样品表面铁离子浓度为3.43×10¹⁸ cm^-3,并通过X射线光电子能谱(XPS)分析了晶体样品中铁元素的离子价态。采用UV/Vis/NIR分光光度计和傅里叶红外光谱仪测试了Fe²⁺∶ZnSe激光晶体的透过谱图。测试结果显示,在3.0 μm处出现了明显的Fe²⁺吸收峰,峰值透过率为5.5%。以波长为2.93 μm的Cr, Er∶YAG激光器为泵浦源,温度77 K时抽运尺寸10 mm×10 mm×4 mm的 Fe²⁺∶ZnSe晶体,获得了能量为191 mJ、中心波长4.04 μm的中红外激光输出,光光转换效率13.84%。     

红外窗口和整流罩材料研究现状与发展趋势

介绍红外窗口的三个综合性能评价因子:热破裂品质因子、光畸变品质因子、抗热冲击品质因子;并用它们评价了氟化镁、尖晶石、氮氧化铝、蓝宝石、硫化锌和硒化锌、金刚石等主要的红外窗口和整流罩材料;综述其国内外的研究现状,并对其未来的发展趋势发表了自己的观点.     

Recent developments in the MOVPE growth of low H content ZnSe-based compounds and heterostructures

The origin of unintentional hydrogen (H) incorporation during metalorganic vapour phase epitaxy (MOVPE) of ZnSe-based compounds is reviewed and discussed. Hydrogen enters in MOVPE-grown ZnSe as a result of alkyls surface reactions, effectively passivating intentional nitrogen (N) acceptors in p-doped ZnSe during the fabrication of blue-light emitting diodes and laser diodes. The existence of a marked trade-off between the proclivity of common Se alkyls to incorporate H and their thermal stability is pointed out. Current strategies to overcome this process limitation are then described along with results achieved and technological drawbacks. The use of a novel class of VI-group alkyl precursors of the form R₂X₂ [where X=Se, S and R is an ethyl (Et) or methyl (Me) radical] is proposed as an alternative solution. These alkyls allow a reduction of H incorporation in ZnSe-based materials, whilst retaining the low temperatures required for the growth of device quality wide band-gap II–VI compounds. Dimethyldiselenide (Me₂Se₂) and diethyldisulphide (Et₂S₂) allow the pyrolytic MOVPE growth of Zn(S)Se compounds below 400 °C. Mass spectrometry fragmentation experiments performed on the alkyl molecular ions allowed to investigate their relative bond strengths and likely decomposition paths. The reduced thermal stability of these alkyls is attributed to a weakening of the XC bonds in the R₂X₂ molecule induced by the stronger XX bond. Secondary ion mass spectrometry (SIMS) analysis showed that as-grown ZnSe have [H]≈(1–3)×10¹⁷ cm⁻³, i.e. among the lowest ever reported for MOVPE-grown layers. The functional validation of the new S and Se alkyls is completed by the structural and optical characterisation of Zn(S)Se-based heterostructures grown on (100)GaAs. High-resolution X-ray diffraction studies are presented along with cathodoluminescence (CL) measurements and compared to what reported in the literature. The epilayer structural properties compare well with that of molecular beam epitaxy and MOVPE grown Zn(S)Se heterostructures. CL spectra of ZnSe epilayers appear of good quality, with pronounced band-edge emissions and reduced deep level contributions. Specific emissions in the spectra of ZnS and ZnSe confirm the occurrence of several impurities in the layers, whose origin can be in part attributed to the yet insufficient purity of the novel alkyls.     

Temperature quenching mechanisms for photoluminescence of MBE-grown chlorine-doped ZnSe epilayers

We report on a detailed investigation on the temperature-dependent behavior of photoluminescence from molecular beam epitaxy (MBE)-grown chlorine-doped ZnSe epilayers. The overwhelming neutral donor bound exciton (Cl⁰X) emission at 2.797 eV near the band edge with a full-width at half-maximum (FWHM) of 13 meV reveals the high crystalline quality of the samples used. In our experiments, the quick quenching of the Cl⁰X line above 200 K is mainly due to the presence of a nonradiative center with a thermal activation energy of 90 meV. The same activation energy and similar quenching tendency of the Cl⁰X line and the I₃ line at 2.713 eV indicate that they originate from the same physical mechanism. We demonstrate for the first time that the dominant decrease of the integrated intensity of the I₃ line is due to the thermal excitation of the “I₃ center”-bound excitons to its free exciton states, leaving the “I₃ centers” as efficient nonradiative centers. The optical performance of ZnSe materials is expected to be greatly improved if the density of the “I₃ center” can be controlled. The decrease in the luminescence intensity at moderately low temperature (30–200 K) of the Cl⁰X line is due to the thermal activation of neutral-donor-bound excitons (Cl⁰X) to free excitons.     

Diode characteristics of Li3N-diffused ZnSe grown by MOVPE

We have fabricated a ZnSe diode using Li₃N diffusion technique for the purpose of forming p-type ZnSe. The maximum hole concentration in the Li₃N-diffused ZnSe layer, which has been grown on a GaAs substrate by metalorganic vapor phase epitaxy, was as high as 10¹⁸ cm⁻³. The ohmic contact to the p-type ZnSe has been demonstrated and the specific contact resistance of Au/p-ZnSe was 1 × 10⁻² Ω · cm². The Li₃N diffusion technique is useful for the bfabrication of ohmic contacts to p-ZnSe.     

Growth process studies by reflectance anisotropy spectroscopy on MOVPE ZnSe

The growth of ZnSe on GaAs by metal organic vapour phase epitaxy (MOVPE) has been studied using reflectance anisotropy spectroscopy (RAS). The RA spectra of ZnSe are significantly different for growth on initially Se- or Zn-exposed GaAs surfaces. The Se-terminated GaAs (001) RA spectrum has Se-dimer-related features at 3.3 and 5.1 eV, and the large, high energy peak dominates during ZnSe growth on this surface. Transmission electron microscopy (TEM) analysis has been used to show that these large RA signals arise from anisotropic surface corrugation of the growing ZnSe epilayer. Under initially Zn-stabilised growth conditions, the ZnSe epilayer RA spectrum is largely featureless, showing only a weak peak at 4.7 eV and a dip at 5.1 eV. The corresponding surface anisotropy is greatly reduced in comparison with growth from the initially Se-terminated surface. These observations reveal RAS to the an important technique for ensuring the desired initial GaAs surface since the grown ZnSe surface morphology is critically dependent on the pre-growth substrate surface treatment. However, as the characteristic ZnSe RA spectra are relatively insensitive to changes in substrate temperature and VI–II ratio, RAS is of more limited use as an in-growth surface probe for MOVPE-grown ZnSe.     

MOVPE Growth of Wide Band-Gap II—VI Compounds for Near-UV and Deep-Blue Light Emitting Devices

We report on the growth by metalorganic vapour phase epitaxy of high structural and optical quality ZnS, ZnSe and ZnS/ZnSe multiple quantum well (MQW) based heterostructures for applications to laser diodes operating in the 400 nm spectral region. High purity ^tBuSH, ^tBu₂Se and the adduct Me₂Zn:Et₃N were used as precursors of S, Se and Zn, respectively. The effect of the different MOVPE growth parameters on the growth rates and structural properties of the epilayers is reported, showing that the crystallinity of both ZnS and ZnSe is limited by the kinetics of the incorporation of Zn, S and Se species at the growing surface. Very good structural and optical quality ZnS and ZnSe epilayers are obtained under optimized growth conditions, for which also dominant (excitonic) band-edge emissions are reported. The excellent ZnS and ZnSe obtained by our MOVPE growth matches the stringent requirements needed to achieve high quality ZnS/ZnSe MQWs. Their structural properties under optimized MOVPE conditions are shown to be limited mostly by the formation of microtwins, a result of the intrinsic high lattice mismatch involved into the ZnS/ZnSe heterostructure. Despite the large amount of defects found, the optical quality of the MQWs turned out to be high, which made possible the full characterization of their electronic and lasing properties. In particular, photopumped lasing emission up to 50 K in the 3.0 eV energy region are reported for the present MQWs heterostructures under power excitation density above 100 kW/cm².     

Characterization of p-type ZnSe grown by MOVPE; excitonic emission lifetime measurements

Time-resolved photoluminescence (TRPL) measurements are made on p-type nitrogen-doped ZnSe grown by photoassisted metalorganic vapor phase epitaxy (MOVPE) together with post-growth thermal annealing, in order to investigate optical quality of the layers. It is suggested that the annealing degrades the layer quality and the MOVPE samples have more non-radiative recombination centers compared with MBE samples. A key issue for high quality p-ZnSe by MOVPE seems to be optimization of annealing conditions.     

Studies on the vapour growth of ZnS,ZnSe and ZnTe single crystals

Large, highly perfect single crystals (up to 10 × 10 × 5 mm³) of ZnS, ZnSe and ZnTe have been grown from the vapour phase by dissociative sublimation and chemical transport with iodine. Good quality crystals were obtained when the growth rate was limited by diffusion of the vapours rather than by thermal convection or by reaction rates at the charge and or the growing surface. The presence of an inert gas and defined iodine concentrations increase the growth stability, especially for charges with slight deviations from stoichiometry. Electronmicrographs, X-ray topographs and etching experiments revealed low dislocation densities and relatively large inclusion-free regions.     

Structural Perfection of ZnSe Crystals Grown by Travelling Heater Method

ZnSe crystals have been grown by the travelling heater method (THM) with PbCl₂ as solvent. Our investigations have shown that ZnSe crystals could be obtained with high crystalline perfection referred to a full width at the half maximum (FWHM) down to 20 arcsec of double crystal rocking curves measured at chemically polished (100)-oriented surfaces. Solvent growth techniques like THM should have a remarkable potential for ZnSe bulk growth if the capture of solute as inclusion and precipitation can be avoided.     

CVT一步生长的ZnSe单晶的光电特性研究

本文采用化学气相输运(CVT)法,由Zn(5N)和Se(5N)一步直接生长了片状ZnSe单晶,并对其结构特性和光电性能进行分析。研究表明,生长出的ZnSe单晶仅显露(111)面,红外透过率约为40%～42%,具有较高的结晶质量。该ZnSe单晶可与In电极形成良好的欧姆接触,其体电阻率约为7.3×109Ω.cm。     

Metalorganic chemical vapor epitaxy and doping of ZnMgSSe heterostructures for blue emitting devices

Blue-green semiconductor laser diodes operating at room temperature are still the domain of wide bandgap II–VI compound semiconductors. CW operation at room temperature and hours of lifetime were reported. However, the conductivity control, defect generation and the ohmic contacts still need improvement. Therefore we focused our work on the MOVPE growth and the optimization of ZnMgSSe/ZnSSe/ZnSe heterostructures as well as on nitrogen doping of ZnSe. To verify the layer quality characterization was carried out by X-ray diffraction, electron probe microanalysis, electrical measurements and photoluminescence. ZnMgSSe/ZnSSe/ZnSe and ZnSSe/ZnSe quantum wells and superlattices were grown to investigate structural as well as interface properties. Electron beam and optical pumping was used to clarify the laser mechanism and to clarify the suitability of a MOVPE process to grow laser quality material. The electrical compensation of ZnSe doped with nitrogen is still controversially discussed whereas high n-type doping with chlorine was reproducible achieved. ZnSe: N doped at different growth conditions (II/VI ratio, growth temperature, nitrogen supply) using N₂ excited in a plasma source or by the use of nitrogen containing precursors was investigated to study the compensation mechanisms.     

ZnSe/ZnCdSe heterostructure nanowires

The authors report the growth of high density ZnSe/ZnCdSe heterostructure nanowires on oxidized Si substrate. It was found that the as-grown nanowires were tapered with mixture of cubic zinc-blende and hexagonal wurtzite structures. It was also found that photoluminescence intensities observed from these ZnSe/ZnCdSe heterostructure nanowires were much larger than observed from the homogeneous ZnSe nanowires. Furthermore, it was found that activation energies for the nanowires with well widths of 6, 12, 18 and 24 nm were 22, 41, 67 and 129 meV, respectively.     

Growth of ZnSe single crystal by CVT method with self-moving convection shield

The self-moving convection shield was used in the growth of ZnSe single crystal by chemical vapor transport method using iodine as a transport agent. The reduction of the convection enables the growth of a 1-in diameter ZnSe single crystal. The incorporation efficiency of iodine on (1 1 1)B facet was proved to be larger than that on (1 0 0) facet. Impurity-hardening effect of incorporated iodine in the grown ZnSe crystal is also suggested.     

化学气相沉积法制备ZnSe微球

采用化学气相沉积方法,以MiSe2为前驱体,制备出尺寸均匀、分散度好的ZnSe微球.通过XRD、EDS和FESEM对产物的结构、成分和形貌进行了测试与表征.结果表明:所得ZnSe微球为立方闪锌矿结构,直径在800～1000 nm之间,具有近于理想的化学计量比.变温光致发光谱研究表明,ZnSe微球在550～640 nm处存在与Zn空位及杂质能级相关的发光峰.     

ZnSe薄膜的化学反应辅助热壁外延法生长及特性研究

本文通过将新型化学气相反应促进剂Zn(NH4)3Cl5引入到热壁外延系统中,以二元素单质Zn和Se为原料,直接在Si(111)衬底上生长了高质量的ZnSe晶体薄膜,薄膜成分接近理想化学计量比。研究了主要工艺参数对薄膜生长形貌和性能的影响。采用SEM、AFM、EDS和PL谱技术研究了生长的ZnSe薄膜的形貌、成分和发光特性。研究结果表明,热壁温度和生长时间是影响ZnSe薄膜形貌的主要因素;气相反应促进剂在薄膜生长和调节成分方面扮演了关键角色,Zn(NH4)3Cl5的存在使得Zn(g)和Se2(g)合成ZnSe晶体的反应转变为气固非一致反应,从而更容易获得近乎理想化学计量比的ZnSe薄膜。ZnSe薄膜在氦镉激光激发下,室温下PL谱由近带边发射和(VZn-ClSe)组合的SA发光组成,而在飞秒激光激发下,仅在481nm处显示出强烈的双光子发射峰。     

单源真空蒸发法制备ZnSe薄膜的实验研究

本文采用单源真空蒸发法制备了ZnSe薄膜,利用电子探针、X射线粉晶衍射等现代测试手段研究了蒸发温度(700～1050 ℃)、基片温度(0～200 ℃)、基片材料(单晶硅、玻璃)以及热处理温度(300～400 ℃)等因素的改变对ZnSe薄膜的成份和结构的影响规律,建立了单源真空蒸发沉积ZnSe薄膜及热处理的实验方法.