EPR studies of point defects in Cu-III–VI2 chalcopyrite semiconductors

EPR and PL spectra were measured to investigate point defects in I–III–VI₂ type chalcopyrite semiconductors where the group I element is Cu. Taking into account various optical spectra, the EPR signals observed were assigned to defect centers involving residual Fe impurities and Cu-vacancies. Some of the point defects were found to form defect-complexes.     

Temperature dependence of band gaps in HgCdTe and other semiconductors

Band-edge shifts induced by the electron-phonon interaction are calculated for HgCdTe alloys and various semiconductor compounds starting from accurate zero-temperature band structures. The calculated temperature variation of gaps agrees with experiments to better than 10% in all materials except InAs and InSb where the deviation is about 50%. While the simple picture that the intra (inter)-band transitions reduce (increase) the gap still holds, we show that both the conduction band edge E_c and valence band edge E_v move down in energy. These shifts in E_v affect the valence band offsets in heterojunctions at finite temperature. The temperature variations of valence band offset and the electron effective mass are also reported.     

T(z) diagram and optical energy gap values of Cd1−zMnzGa2Se4 alloys

The T(z) diagram of the system Cd_1−zMn_zGa₂Se₄ was obtained from x-ray diffraction and differential thermal analysis measurements. It was found that at lower temperatures, a single phase solid solution occurs across the whole compositional range and values of lattice parameters were determined as a function of z. At higher temperatures, an order-disorder transition occurs, in the range 0 < z < 0.6 to a partially ordered tetragonal structure and for 0.6 < z < 1. 0 to a disordered defect zinc-blende structure. In the T(z) diagram, both the ordering boundary and the solidus curve appear to show discontinuities at z = 0.6, corresponding to the change in the disordered phase. It is suggested that the symmetries of the terminal compounds are different one from the other. Optical absorption measurements were made at 300 K to show the variation of the direct optical energy gap E_o with z, and again the values appear to divide into two parts below the above z = 0.6.     

T(z) phase diagram and optical energy gaps in CuGa(Se z Te1−z )2 alloys

TheT(z) phase diagram of the system CuGa(Se _z Te_1-z )₂ was obtained from x-ray diffraction and differencial thermal analysis (DTA) measurements. DTA measurements were carried out on each sample and the transition temperatures were plotted as a function of alloy composition. Values of lattice parameter were determined in all cases. Values of the optical energy gap at 300 K were obtained from optical absorption measurements, and these were analysed by using a recently proposed model which explains the downward bowing observed in the I-III-VI₂ alloys.     

使用Na_2CO_3/NaHCO_3体系进行单晶硅制绒

通过单晶硅表面制绒可以降低太阳能电池面板对光的反射率进而提高电池的转化效率。利用Na2CO3、NaHCO3和Na2CO3/NaHCO3溶液进行了单晶硅表面制绒,并利用扫描电子显微镜和紫外/可见光光度计对所得绒面的形貌及反色率分别进行了分析。研究了溶液浓度、溶液组成及反应时间等因素对所制单晶硅绒面反射率的影响。结果表明:在Na2CO3:NaHCO3质量比为10:1,反应温度为85℃,反应时间为10 min时,可获得反射率为15.22%的绒面。     

Comparison of dry etching of III-V semiconductors in ICl/Ar and IBr/Ar electron cyclotron resonance plasmas

ICl/Ar and IBr/Ar plasmas were found to be promising candidates for room temperature dry etching processing of the III-V semiconductors GaAs, AlGaAs, GaSb, InP, InGaAs, and InSb. Results showed fast etch rates (0.7 μm/min in ICl/Ar and −0.3 μm/min in IBr/Ar), and at high microwave power, 1000 W, good surface morphology (typical root mean square roughness ∼2 nm), while retaining the near-surface stoichiometry, especially in IBr/Ar plasmas. There was little change of surface smoothness over a wide range of plasma compositions for Gacontaining materials in both ICl/Ar and IBr/Ar plasmas, (e.g. GaAs), while there was a window region with about 25–50% of IBr in IBr/Ar plasmas to maintain good morphology of In-containing semiconductors like InP. Selectivities of 4–10 over mask materials such as SiO₂, SiN_x, and W were typical in ICl/Ar plasmas.     

Etching of As- and P-based III–V semiconductors in a planar inductively coupled BCl<Subscript>3</Subscript>/Ar plasma

A parametric study of the etch characteristics of Ga-based (GaAs, GaSb, and AlGaAs) and In-based (InGaP, InP, InAs, and InGaAsP) compound semiconductors in BCl₃/Ar planar inductively coupled plasmas (ICPs) was performed. The Ga-based materials etched at significantly higher rates, as expected from the higher volatilities of the As, Ga, and Al trichloride, etch products relative to InCl₃. The ratio of BCl₃ to Ar proved critical in determining the anisotropy of the etching for GaAs and AlGaAs, through its effect on sidewall passivation. The etched features in In-based materials tended to have sloped sidewalls and much rougher surfaces than for GaAs and AlGaAs. The etched surfaces of both AlGaAs and GaAs have comparable root-mean-square (RMS) roughness and similar stoichiometry to their unetched control samples, while the surfaces of In-based materials are degraded by the etching. The practical effect of the Ar addition is found to be the ability to operate the ICP source over a broader range of pressures and to still maintain acceptable etch rates.     

(Bi2Te3)0.90(Sb2Te3)0.05(Sb2Se3)0.05热压合金微观结构和电学性能相关性研究

通过熔炼,研磨制备N型(Bi2Te3)0．90(Sb2Te3)0．05(Sb2Se3)0．05热电材料的粉末,热压制备混合粉末热压合金。通过SEM和XRD研究热压合金的微观结构,在室温测量热压合金样品的电学性能。结果表明热压合金在微观结构和电学性能上存在各向异性,从而预示能够在增强材料机械强度的同时提高其热电性能。     

Observation of lasing from Cr2+:CdTe and compositional effects in Cr2+-doped II-VI semiconductors

We are engaged in a systematic study of the optical and laser properties of Cr²⁺-doped cadmium chalcogenides. Previously, we demonstrated quasi-continuous wave lasing from Cr²⁺-doped Cd_0.55Mn_0.45Te with slope efficiencies as high as 64% and a laser tuning range from 2,170–3,010 nm. In this paper, we report the first demonstration of lasing from Cr:CdTe at room temperature. Pulsed-laser operation was obtained with a free-running spectrum centered at 2,535 nm. The slope efficiency of the laser was low (∼1%) because of large parasitic losses at the laser wavelength. The spectroscopic properties of Cr:CdTe are favorable for laser applications because of a large emission cross section (∼2.5 × 10⁻¹⁸ cm²) and a high emission-quantum yield (∼88%). In addition, CdTe can easily incorporate Cr ions either through melt growth or diffusion doping. Along with our results on Cr²⁺:CdTe, we report on the optical properties of several other Cr²⁺-doped II-VI semiconductors (ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, Cd_0.9Zn_0.1Te, Cd_0.65Mg_0.35Te, Cd_0.85Mn_0.15Te, and Cd_0.55Mn_0.45Te) and compare them for applications as solid-state laser materials.     

Formation and characterization of CdS/ZnSiAs2 heterojunctions

A rectifying junction between MOCVD formed ZnSiAs₂ and evaporated CdS has been studied. Current-voltage behavior at current densities above about 1mA/cm² appears to be dominated by tunnelling. Capacitance measurements indicate an acceptor concentration in ZnSiAs₂ of 5 × 10¹⁶cm^-3, junction diffusion voltage of 1.0V and the presence of deep traps. Device series resistance could be attributed in part to compensating cross-doping. CdS/ZnSiAs₂ junctions exhibit photovoltaic response, and photovoltages above 0.5V under 5 sun illumination. ZnSiAs₂ electron affinity is estimated to be 3.9eV, and a tentative CdS/ZnSiAs₂ band diagram is presented.     

Elastic and optoelectronic properties of novel Ag3AuSe2 and Ag3AuTe2 semiconductors

Ag₃AuSe₂ and Ag₃AuTe₂ are interesting class of semiconducting materials. Here, elastic and opto-electronic properties of Ag₃AuSe₂ and Ag₃AuTe₂ semiconductors are studied in detail using density functional theory. Different schemes are selected to treat the exchange-correlation effects. The unit cell of the compounds is fully optimized and calculated cell constants are found in agreement to the existing experimental data. The calculated elastic constants and elastic moduli reveal that the compounds possess ductile nature and are elastically stable. It is found that both compounds are direct bandgap semiconductor with bandgap value of 1.009 eV for Ag₃AuSe₂ and 0.551 eV for Ag₃AuTe₂. As the compounds have narrow and direct bandgaps, therefore optically active. The optical properties like reflectivity, absorption coefficient, energy loss function, refractive index including and complex dielectric function are studied in detail. The direct band gap nature of these compounds make them useful candidate for different devices applications.     

Mechanical and electronic properties of Si,Ge and their alloys in P42/mnm structure

Structural, mechanical, and electronic properties of Si–Ge alloys in P4₂/mnm structure were studied using first-principles calculations by Cambridge Serial Total Energy Package (CASTEP) plane-wave code. The calculations were performed with the local density approximation and generalized gradient approximation in the form of Perdew–Burke–Ernzerhof, PBEsol. The calculated excess mixing enthalpy is positive over the entire germanium composition range. The calculated formation enthalpy shows that the Si–Ge alloys are unstable at 0 K; however, the alloys might exist at specified high temperature scale. The anisotropic calculations show that Si₁₂ in P4₂/mnm structure exhibits the greatest anisotropy in Poisson’s ratio, shear modulus, Young’s modulus and the universal elastic anisotropy index A^U, but Si₈Ge₄ has the smallest anisotropy. The electronic structure calculations reveal that Si₁₂ and Si–Ge alloys in P4₂/mnm structure are indirect band gap semiconductors, but Ge₁₂ in P4₂/mnm structure is a direct semiconductor.     

Al2O3 stacks on In0.53Ga0.47As substrates: In situ investigation of the interface

In this work we present an in situ investigation of the interface composition between an In_0.53Ga_0.47As substrate and an Al₂O₃ oxide grown by molecular beam deposition in ultra high vacuum conditions. In the effort to improve the chemical quality of the interface, reduction of semiconductor-oxygen bonding at the interface can be obtained by growing a few Å thick pure Al layer before starting exposure of the surface to the atomic oxygen flux. Conversely, when a Ge interface passivation layer is intercalated between the semiconductor and the oxide stack, the interface chemistry is governed by Ge reaction with other species (Al, O), leading only to a partial suppression of the interface oxides.     

EPR studies of native and impurity-related defects in II–IV–V2 semiconductors

Magnetic resonance studies of native defects in Zinc germanium diphosphide (ZnGeP₂) and their energy level positions in the band gap are reviewed and first results on defects in ZnSiP₂ are presented. The contribution of the dominant native defects to the optical absorption of ZnGeP₂ crystals is revealed by photo-EPR investigations in combination with the first ODMR experiments. The EPR results published for Mn and Fe in the II–IV–V₂ chalcopyrites are summarized. The observation of some new Mn centers and the first experimental detection of antiferromagnetic Mn–Mn coupled pairs in ZnGeP₂ are presented. In addition, new results concerning Mn-induced local changes of the free parameter x_f of the chalcopyrite structure at the impurity site are discussed.     

Surface mobility and distribution of electrons in the accumulation layer of Ga2Se3/GaAs heterostructures

The dependence of the electron drift mobility in the undepleted conduction channels of Ga₂Se₃/GaAs heterostructures on the surface charge density is measured. The presence of charge coupling in the accumulation layer sufficient for creating electrical (or microelectronic) devices is discovered. Fiz. Tekh. Poluprovodn. 32, 718–720 (June 1998)     

Laser direct writing of β-Co/Ga and Mn/Ga alloy microstructures from organometallic single-source precursors

β-Co/Ga and Mn/Ga alloys have been deposited on various substrates by laser direct write chemical vapour deposition (LCVD) from novel single-source precursors. The preformed alloy stoichiometry of 1:1 defined by the metal ratio of the precursors, (CO)₄Co-GaEt₂(NMe₃) (1) and (CO)₅Mn-GaEt₂(NMe₃) (2), is retained within the deposited structures. The depositions were up to 1.5 μm thick and the lateral dimension (4 μm) was determined by the diameter of the laser focus. The deposited structures were contaminated with ∼10 at. % C and O (by AES).     

Investigation of pyroelectric characteristics of 0.8 Pb (Zn1/3Nb2/3)O3 - 0.1 Pb TiO3 - 0.1 BaTiO3 ceramics with special reference to uncooled infrared detection

The pyroelectric characteristics for 0.8 Pb(Zn_1/3Nb_2/3)O₃ - 0.1 PbTiO₃ - 0.1 BaTiO₃ ceramics were investigated to determine the usefulness of this material as an uncooled infrared detector. Two successive phase transitions, changing the crystal symmetry from rhombohedral to tetragonal, and then to cubic on a heating process, were observed in the material. The results of measurements were compared with those of PLZT (8/40/60) and the Ca-Modified PbTiO₃, which are currently the favored materials for uncooled arrays. The results indicate that 0.8 PZN - 0.1 PT - 0.1 BT is a promising material for both transverse mode and pyroelectric CCD arrays.     

The phase relations in the system Tl2Se-As2Se3 and the crystal growth of Tl3AsSe3

The phase diagram for the system T12Se-As2Se3 was studied by quenching and thermal analysis experiments, with emphasis on the composition range 15 to 35 mol % As₂Se₃, so as to determine the melting relations of Tl₃AsSe₃, a useful compound for optical and acousto-optical devices. Tl₃AsSe₃ melts congruently at 311 ± 2‡C, and the only other pseudobinary compound, TlAsSe₂, melts congruently at 272 ± 2‡C. Eutectics lie between Tl₂Se and Tl₃AsSe₃ (∿ 21 mol % As₂Se₃, 302 ± 2‡), between Tl₃AsSe₃ and TlAsSe₂ (∿ 32 mol % As₂Se₃, 238 ± 3‡), and between TlAsSe₂ and As₂Se₃ (∿ 72 mol % As₂Se₃, 249 ± 3‡). The maximum-melting Tl₃AsSe₃ composition lies at 24.62 + 0.13 mol % As₂Se₃. Crystals of Tl₃AsSe₃ were grown from three pseudobinary compositions with the best crystals obtained from melts containing 24.62 mol % As₂Se₃. This research was sponsored by the Advanced Research Projects Agency of the Department of Defense and was monitored by the Air Force Materials Laboratory, LP, under Contract No. F33615-72-C-1976     

Surface cleaning and etching of CdZnTe and CdTe in H2/Ar, CH4/H2/Ar, and CH4/H2/N2/Ar electron cyclotron resonance plasmas

This paper compares H₂/Ar, CH₄/H₂/Ar, and CH₄/H₂/N₂/Ar plasma etch processes for CdZnTe and CdTe substrates in view of their potential to provide high-quality substrate surfaces for subsequent HgCdTe epitaxy. An electron cyclotron resonance source was used as plasma generator, and ellipsometry, angle-resolved x-ray photoelectron spectroscopy and low energy electron diffraction were applied to characterize roughness, composition, and order of the resulting substrate surfaces. It was found that CdZnTe is much more susceptible to evolving surface roughness under H₂/Ar plasma exposure than CdTe. The severe roughening observed at 100°C sample temperature was found to be correlated with a buildup of ZnTe at the surface, which suggests that the roughness formation may result from a preferential etching of the CdTe component. This surface degradation could be reduced by the addition of CH₄ to the process gases. However, only a further addition of nitrogen gas balanced and substantially improved the plasma process so that atomically clean, very smooth, and stoichiometrically composed CdZnTe surfaces of long-range order were eventually obtained.