Effect of additionally introduced Zn and Eu dopants on the photoluminescence spectra of Er-Doped GaN crystals

It is shown that the effect of dopants on the photoluminescence spectrum depends on the conductivity type of the initial GaN crystals. Sensitization of emission is observed in wurtzite p-GaN crystals doped with Er. The same effect was previously observed in such crystals doped with Eu and Zn. In n-type GaN crystals sequentially doped with Eu, Zn, and Er, emission is observed in the visible (λ = 360–440 and 530–560 nm) and IR (λ = 1.54 μm) spectral regions.     

Spatial distribution of defects and the kinetics of nonequilibrium charge carriers in GaN wurtzite crystals doped with Sm,Eu, Er,Tm, and supplementary Zn impurities

By analyzing time-resolved and steady-state photoluminescence spectra, it is established that the spatial distribution of rare-earth ion dopants in wurtzite GaN crystals doped with Sm, Eu, Er, or Tm is governed by the type and concentration of defects in the initial semiconductor matrix as well as by the type of the impurity (its capacity for segregation). Doping with multicharged rare-earth impurities and additionally introduced Zn impurity leads to an intensification of emission. The effect of intensification of emission in the case of n-and p-GaN crystals is considered with the use of the model of isoelectronic traps.     

Impurity centers of rare-earth ions (Eu,Sm, Er) in GaN wurtzite crystals

Gallium nitride (GaN) was doped with Eu, Sm, and Er impurities using the diffusion method. The behavior of rare-earth impurities (the formation of donor or acceptor levels in the GaN band gap) correlates with the total concentration of defects, which is determined from optical measurements, and with the position of the Fermi level in starting and doped crystals. The intensity of emission lines, which are characteristic of the intracenter f-f transition of rare-earth ions, is controlled by the total defect concentration in the starting semiconductor matrix.     

UV and IR emission intensity in ZnO films,nanorods, and bulk single crystals doped with Er and additionally introduced impurities

For ZnO films, nanorods, and bulk single crystals doped with Er⁺ ions, it is shown that the effect of codopants introduced into the cation and ion sublattices and the observation of a high-intensity emission band at the wavelength λ_max = 1535 nm are defined by the local environment of the Er⁺ ion. Doping of the films and single crystals with Er⁺ ions by diffusion brings about an infrared (IR) emission band with a low intensity because of an inadequate concentration of impurity ions. The emission intensity of this band can be raised by introducing additional Ag, Au, or N⁺ impurities into the ZnO films. The UV-emission intensity of the Er-doped films and single crystals at λ_max = 368–372 nm is identical to that of the undoped films. ZnO nanorods doped with Er only or together with Al or Ga codopants exhibit only one IR band (at λ_max = 1535 nm), whose intensity decreases upon the introduction of codopants. Doping of the nanorods with the N⁺ gaseous impurity during growth (930 < T < 960°C) and then with the Er⁺ impurity by diffusion does not yield a substantial increase in the IR-emission intensity compared to the that of the corresponding band for nanorods not doped with the N⁺ impurity. In the Er-doped nanorods, whose photoluminescence spectra exhibit a high-intensity band at λ_max = 1535 nm, the UV emission band at λ_max = 372 nm is practically lacking.     

利用近场光谱研究GaN蓝光二极管的杂质发光

运用近场光谱方法研究了在蓝宝石衬底上用低压ＭＯＣＶＤ方法外延生长的ＧａＮ蓝光二极管的杂质发光光谱。研究结果表明近场光谱为研究样品表面微观发光机理中提供了一个有力的手段,它能够同样品表面微区空间分辨的局域光谱信息。本文给出了研究中所观察到的一些实验现象,并对近场光谱中各发光峰的强度随注入电流变化关系进行了深入研究。     

Metastable states in InGaN/GaN MQW structures doped with Sm, Eu, and Eu + Sm

Measurements of the microphotoluminescence (microPL) spectra of InGaN/GaN:Sm and InGaN/GaN:Eu quantum well (QW) structures show that the action of a magnetic field gives rise to Van Vleck paramagnetism for Eu³⁺ and Sm³⁺. The macrophotoluminescence (macroPL) spectra recorded after measuring the microPL spectra of InGaN/GaN QW structures doped with Sm or Eu + Sm at a high excitation level (>10²³ photons cm^?2 s^?1) in magnetic fields contain no QW emission lines which are present in the macroPL spectra recorded before these microPL measurements. This is indicative of the presence of photoinduced defects. Annealing of the InGaN/GaN:Sm and InGaN/GaN:(Eu + Sm) structures reduces the concentration of photoinduced defects.     

未掺杂GaN外延膜的结晶特性与蓝带发光关系的研究

采用卢瑟福背散射／沟道技术，X射线双晶衍射技术和光致发光技术对几个以MOCVD技术生长的蓝带发光差异明显的未掺杂GaN外延膜和GaN：Mg外延膜进行了测试。结果表明，未掺杂GaN薄膜中出现的2．9eV左右的蓝带发光与薄膜的结晶品质密切相关。随未掺杂GaN的蓝带强度与带边强度之比增大，GaN的卢瑟福背散射／沟道谱最低产额增大，X射线双晶衍射峰半高宽增大。未掺杂GaN薄膜的蓝带发光与薄膜中的某种本征缺陷有关。研究还表明，未掺杂GaN中出现的蓝带与GaN：Mg外延膜中出现的2．9eV左右的发光峰的发光机理不同。     

Refractive indices of wurtzite and zincblende GaN

Refractive index measurements on both wurtzite and zincblende GaN films grown by plasma-enhanced molecular beam epitaxy are reported. For birefringent uniaxial wurtzite GaN samples the index of refraction was measured along the crystalline axis. In this direction the index is 2.78 at 3.4 eV. For cubic GaN films grown on GaAs substrates, the refractive index is 2.91 at 3.2 eV. Estimation of the confinement factor for optimised waveguides based a combination of III-V nitrides indicates very favourable values for laser operation.<>     

Cr掺杂纤锌矿GaN的磁性和光学性质

采用自旋极化密度泛函理论方法,对Cr掺杂纤锌矿GaN的能带结构和态密度进行计算,通过计算的能带结构和光学线性响应函数,系统讨论了Cr掺杂对纤锌矿GaN电子结构、磁学和光学属性的影响。计算结果显示:Cr掺杂纤锌矿GaN的反铁磁态具有半金属特征,铁磁态具有金属特性和磁性,磁矩主要源于费米能级附近的Cr 3d和N 2p能带发生劈裂导致自旋向上和自旋向下的电子的态密度不同所致。光学性质计算结果显示,Cr掺杂纤锌矿GaN的费米能级附近出现极大的介电峰,具有优异的发光性能,峰值对应于紫外波段,在高能区吸收峰发生了红移现象,在低能区红外波吸收增强。理论计算表明,Cr掺杂纤锌矿GaN可能是一种性能优异的磁光材料。     

Study of the impurity photoconductivity and luminescence in ZnSe:Ni crystals in the visible spectral region

The photoconductivity and photoluminescence spectra of ZnSe:Ni crystals in the visible spectral region are studied. It is established that the high-temperature impurity photoconductivity of ZnSe:Ni crystals is controlled by the optical transitions of electrons from the ground state ³ T ₁(F) to high-energy excited states, with subsequent thermally activated transitions of electrons to the conduction band. A photoconductivity band associated with the photoionization of Ni impurities is revealed. The intracenter luminescence of ZnSe:Ni crystals is efficiently excited with light corresponding to the intrinsic absorption region of Ni²⁺ ions.     

The edge ultraviolet luminescence of GaN:Zn films activated in a nitrogen plasma

The effect of annealing in nitrogen plasma on the photoluminescence and photoconductivity spectra, conduction type, and the surface morphology of gallium nitride films doped with zinc was studied. Emergence of intense ultraviolet edge emission peaking at a wavelength of 376 nm was observed after a high-temperature annealing in nitrogen plasma was detected. An appreciable suppression of blue donor-acceptor and excitonic photoluminescence in annealed GaN:Zn samples was observed.     

Defect-related luminescence of GaN:Zn films thermally treated in a radio-frequency ammonia plasma

The effect of thermal annealing in nitrogen radicals obtained by the treatment of NH₃ in a radio-frequency discharge on the luminescence properties of GaN:Zn films grown by MOCVD/hydride epitaxy on sapphire (0001) substrates is investigated. As the thermal treatment temperature was increased, a steady weakening of the violet (2.88 eV) and near-edge (3.48 eV) photoluminescence bands was observed. As a result of the thermal treatment in nitrogen radicals at 500–750°C, new bands that peaked at 3.27 and 3.42 eV were detected; the intensities of these bands increased with increasing treatment temperature. The mechanism of formation and the origin of all the bands are analyzed comprehensively. It is found that the luminescence bands at 2.88, 3.42, and 3.27 eV are characteristic of the GaN films obtained by practically each technology and are associated with the simple structural defects. The participation of O in the formation of the band at 3.42 eV is proved experimentally.     

Activation-controlled conduction and metal-insulator transition in the impurity band of narrow-gap p-Hg1−x CdxTe doped crystals

Metal-insulator transition and hopping conduction are studied in narrow-gap copper-doped p-Hg_1?x Cd_xTe crystals in a wide range of temperatures, compositions x, and impurity concentrations. It is shown that, as distinct from wide-gap semiconductors, a characteristic size of shallow acceptor wave function responsible for the hopping mechanism of conduction is determined by the effective mass of a heavy, rather than light, hole. The presence of low-temperature ?₂-conduction over the delocalized states of positively charged acceptors near the metal-insulator transition is established.     

Studies of the infrared luminescence of ZnSe doped with copper and oxygen

The results of studying the poorly understood 700-to 2000-nm spectral region in ZnSe cathodoluminescence of condensates deposited from the vapor phase with deviations from stoichiometry and Cu and O introduction into a pure matrix are reported. The nature of cathodoluminescence in the region of 1300–1400 nm is refined: the conclusion is drawn that the emission is caused by isolated V _Zn ^I(II) vacancies. The behavior of V _Se-related luminescence bands at 830 and 960 nm, when the matrix composition changes, is considered.     

Investigation of MOVPE-grown GaN layers doped with As atoms

Conditions are investigated for the injection of arsenic into gallium nitride layers grown by metal-organic vapor-phase epitaxy. It is shown that the deposition of GaAs on a GaN surface relieves stresses in the GaN layer. The high-temperature overgrowth of a thin GaAs layer by a GaN layer causes As atoms to diffuse into the GaN, produces a thick, homogeneously doped GaN:As region, and creates a bright band in the photoluminescence spectrum with a maximum at ∼2.5 eV. Fiz. Tekh. Poluprovodn. 33, 791–794 (July 1999)     

TEM和CL准原位表征GaN单根纳米线中WZ/ZB结构及其发光特性

纤锌矿（WZ）/闪锌矿（ZB）结构以及WZ/ZB超结构广泛存在于一维Ⅲ-Ⅴ族半导体材料中。本文采用TEM和CL（阴极荧光谱）准原位表征的方法,对GaN纳米线的各种结构进行了系统的表征,并且建立了材料纳米结构与对应发光性质之间的直接联系。研究发现相对于纯WZ结构的GaN单根纳米线,具有WZ/ZB结构纳米线的CL出现了蓝移。通过对CL发光谱的蓝移现象的分析和研究表明,蓝移是由于高密度的WZ/ZB结构单元及其各种超结构所引起的特殊效应。     

Self-consistent calculation of mode spectra and modulation responsein wurtzite GaN quantum-well lasers

The photon rate-equation formalism is used to evaluate the multimode photon density, the output lasing power, and the modulation frequency response in pseudomorphically strained wurtzite GaN quantum-well lasers. The formalism is based on a self-consistent methodology that couples an envelope function (or k·p) Hamiltonian with Poisson's equation. From this approach, we consider (1) the band structure under the influence of large piezoelectric fields and with many-body effect; and (2) the stimulated and spontaneous emissions for each Fabry-Perot mode. Our calculations predict a threshold current density of approximately 1 kA/cm² and an intrinsic 3-dB modulation bandwidth of 11.7 GHz at 40-mW output power for a 50-Å pseudomorphically strained GaN-Al_0.2Ga_0.8N single-quantum-well (SQW) laser. Our estimation of the threshold current density represents the theoretical limit and is compatible with recent experimental results in InGaN multiple-quantum-well (MQW) lasers     

Optical spectra of Eu2+ ion doped KMgF3 single crystals grown by Bridgman method

High-quality KMgF3 single crystal containing 0.5 mol% europium (Eu) was prepared by an improved Bridgman method. X-ray diffraction (XRD), photoluminescence spectra and fluorescence lifetime were measured. The results indicate the reduction of Eu3+ to Eu2+ in the KMgF3 single crystal. Under the excitation of 259 nm, 370 nm and 394 nm, the sample has two distinct emissions of Eu2+:4f7→4f7(~363 nm) and 4f65d1→4f7 (~440 nm). The substitution site for Eu ion is confirmed. The optical property investigation result shows that the Eu2+ doped KMgF3 single crystal may be used as potential laser media and related materials for optical devices.     

Photoconductivity of CdS films,undoped and doped with alkali-metal impurity ions

The nonequilibrium electron processes that occur during photoconductivity increase and relaxation in pyrolytic CdS films, both nominally undoped and doped with alkali metals, are studied. The photocurrent increase and relaxation are slow. In some cases, the experimental curve describing the photoconductivity increase is S-shaped or exhibits several thresholds. The dependence of the steady-state photocurrent on the excitation intensity is superlinear. The introduction of alkali-metal impurities increases the photocurrent in the CdS films by up to an order of magnitude compared to the photocurrent in the undoped films. The experimentally observed features of the photoconductivity kinetics of the structures under study are attributed to the profound effect of trapping centers of several types on the behavior of nonequilibrium charge carriers.     

Effect of electron and neutron bombardment on the orange luminescence spectra of not specially doped and copper-doped cadmium sulfide single crystals

CdS single crystals which were not specially doped and which were doped with copper (N _Cu=10¹⁸ cm⁻³) have been investigated. It is concluded on the basis of an analysis of the dose dependences of the orange luminescence intensity (λ _M=605 nm) of “pure” and doped samples upon bombardment by electrons with E=1.2 MeV and by fast reactor neutrons that the centers responsible for this luminescence are complex in nature. They consist of interstitial cadmium atoms and oxygen atoms. Electron bombardment of CdS:Cu single crystals results in the formation of new centers which are responsible for luminescence with λ _M=570 and 545 nm. Fiz. Tekh. Poluprovodn. 31, 390–392 (April 1997)