Optical responses of ZnSe quantum dots in silica gel glasses

The characteristic features of the absorption and photoluminescence spectra of ZnSe quantum dots (QDs) inside a silica matrix derived from a sol-gel method were studied at room temperature. Compared with the bulk materials, the absorption edges of ZnSe QDs in silica gel glass were shifted to higher energies and the spectra exhibited the discrete excitonic features due to the quantum confinement effects. Besides the band-edge emission, photoluminescence at ultraviolet excitation also showed the emissions related to the higher excitonic states. (C) 2004 Elsevier B.V. All rights reserved.

STUDY OF RAMAN-SPECTRA OF ZNSE-ZNTE STRAINED LAYER SUPERLATTICES

The Raman spectra of the II-VI wide band-gap compound ZnSe-ZnTe semiconductor strained-layer superlattices have been studied. The relations between the Raman shifts of the longitudinal optical phonon modes and the superlattice-structure parameters have been determined. When the layer thickness exceeds 40 angstrom, the change of the LO phonon-mode frequency shifts with the layer thickness is minimal, whereas when the layer thickness is smaller than 40 angstrom, great shifts have been observed. We estimate that the critical thickness of ZnSe-ZnTe SLS is about 40 angstrom. We have also found that the shifts induced by strain are much larger than the red shifts due to confinement.

INDIUM OHMIC CONTACTS TO N-ZNSE

The reaction between an indium over layer and high purity MBE grown n-ZnSe chlorine doped (2x 10(18) cm-3) epilayers has been investigated using X-ray diffraction, Rutherford backscattering spectroscopy, X-ray photoelectron and Auger electron spectroscopy, and by electrical function tests (I-V and C-V). Good ohmic contacts were formed after annealing at 250 or 300-degrees-C for a few minutes in forming gas. Annealing at lower or higher temperatures resulted in higher resistance or rectifying contacts. The data show that no compounds were formed at the interface; instead In appeared to diffuse into the ZnSe. High surface doping densities appear to allow an ohmic contact, but the electrical data suggest that compensation effects are also very significant in the formation of the contact. These effects must be considered for successful formation of the ohmic contact.

Luminescence properties of ZnSe films grown by hot wall epitaxy

The photoluminescence (PL) properties of ZnSe films grown by hot wall epitaxy are reported. The PL spectra show clear neutral donor-bound exciton peak; donor acceptor pair (DAP) peak, conduction band to acceptor (CA) peak, and their phonon replicas until fourth order. The conduction band to acceptor peak and it's phonon replicas exist until room temperature. From the ratio of PL intensities of DAP and CA peaks and their replicas, we obtain the Huang-Rhys factor S = 0.58, in agreement with other experiments for acceptor-bound exciton transitions. From the temperature dependence of PL intensities we derive the activation energy of thermal quenching process for the DAP transitions as about 7 meV.

PRESSURE-DEPENDENCE OF PHOTOLUMINESCENCE FROM ZNSE-TE-(CDSE)(1) (ZNSE)(3) SUPERLATTICE QUANTUM-WELLS

Pressure dependence of photoluminescence from ZnSe:Te-(CdSe)(1)(ZnSe)(3) short period superlattice quantum wells is reported. In addition to the exciton band from the superlattice layers, strong bands for localized excitons self-trapped al single Te (Te-1) atom, double Te atoms (Te-2) and Te clusters (Te-n, n greater than or equal to 3) as well as for the free excitons in isoelectronic Te incorporated ZnSe layers are observed. Significant differences in the pressure and temperature dependencies of the observed exciton transitions are presented and discussed.

分子束外延生长ZnSe自组织量子点光、电行为研究

分别应用光致发光、电容－电压和深能级瞬态傅里叶谱技术说细研究ZnSe自组织量子点样品的光学和电学行为。光致发光温度关系表明ZnSe量子点的光致发光热猝火过程机理。两步猝火过程的理论较好模拟和解释了相关的实验数据。电容－电压测量表明样品表观载流子积累峰出现的深度（样品表面下约100nm处）大约是ZnSe量子点层的位置。深能级瞬态傅里叶谱获得的ZnSe量子点电子基态能级位置为ZnSe导带下的0.11eV，这与ZnSe量子点光致发光热猝火模型得到的结果一致。

AnSeTe/ZnSe量子阱中Te等电子陷阱的静压光子发光谱研究

测量了ZnSe_(0.92)Te_(0.08)/ZnSe超晶格量子阱材料在77K时0～7.8GPa静压下的光致发光谱。观察到AnSe_(0.92)Te_(0.08)阱层中Te等电子陷阱上的束缚激子发光，发现它的压力系数比ZnSe带边发光的压力系数小约50%，表明Te等电子陷阱对激子的束缚势是相当局域的。还观察到了激子在ZnSe_(0.92)Te_(0.08)阱层中的Te等电子陷阱能级与相邻（CdSe）_1/(ZnSe)_3短周期超晶格之间的转移现象。

掺氮ZnSe外延层的光致发光研究

国家自然科学基金

温度引起的ZnSe/Zn_（0.84）Mn_（0.16）Se超晶格中势阱层和势垒层的反转

测量了ZnSe，Zn_(0.84)Mn_(0.16)Se合金和ZnSe/Zn_(0.84)Mn_(0.16)Se超晶格的10～300K的变温光致发光谱。发现ZnSe的带隙在10K时比Zn_(0.84)Mn_(0.16)Se合金的带隙小，而在300K时比合金的带隙大。预计ZnSe/Zn_(0.84)Mn_(0.16)Se超晶格中在130K附近会发生势阱层和势垒层的反转。在ZnSe/Zn_(0.84)Mn_(0.16)Se超晶格中观测到了这种反转但发生在80K附近。超晶格中Zn_(0.84)Mn_(0.16)Se层的应变可能是反转温度变低的原因。