GaAs1—xPx晶体生长

最近Ⅲb—Ⅴb族化合物半导体做为注入型发光元件材料,已被广泛地应用。其中最引人注意的可见发光材料是Ga_1—xAlxAs、GaAs_1—xPx、GaP等含Ga的化合物半导体。从晶体生长方法,发光区域的形成方式以及发光特性来看,这些化合物都具有自己     

Resonant excitation of nitrogen bound excitons in Ga As1−xPx alloys

The luminescence spectra at 18 K of nitrogen-bound exciton in Ga As_1−xP_x; x = 0.59 excited with the energy 2.540 eV show bands that lay in an energy range of about 136 meV. Luminescence spectra obtained with resonant excitation energies show sharp lines that appear on the band's energy range. They are attributed to TA^X, LA^X, 2TA^X, LO^loc, TO^Γ_p and LO^Γ_p modes. These lines have different relative-intensities. In this paper, we identify phonon peaks and we give a possible interpretation of different recombination processes.     

Fundamental studies and device application of δ-doping in GaAs Layers and in AlxGa1−xAs/GaAs heterostructures

In addition to the realization of atomically abrupt interfaces in III–V semiconductors by molecular beam epitaxy, the confinement of donor and acceptor impurities to an atomic plane normal to the crystal growth direction, called-doping, is important for the fabrication of artifically layered semiconductor structures. The implementation of-function-like doping profiles by using Si donors and Be acceptors generates V-shaped potential wells in GaAs and Al_xGa_1–xAs with a quasi-two-dimensional (2D) electron (or hole) gas. In this review we define three areas of fundamental and device aspects associated with-doping. (i) The prototype structure of-doping formed by a single atomic plane of Si donors in GaAs allows to study the 2D electron gas by magnetotransport and tunneling experiments, to study the metal-insulator transition, and to study central-cell and multivalley effects. In addition, non-alloyed ohmic contacts to GaAs and GaAs field-effect transistors (-FETs) with a buried 2D channel of high carrier density can be fabricated from-doped material. (ii) GaAs sawtooth doping superlattices, consisting of a periodic sequence of alternating n- and p-type-doping layers equally spaced by undoped regions, emit light of high intensity at wavelengths of 0.9 < <1.2 [m], which is attractive for application in photonic devices. The observed carrier transport normal to the layers due to tunneling indicates the feasibility of this superlattice as effective-mass filter. (iii) The confinement of donors (or acceptors) to an atomic (001) plane in selectively doped Al_xGa_1–xAs/GaAs heterostructures leads to very high mobilities, to high 2D carrier densities, and to a reduction of the undesired persistent photo-conductivity. These-doped heterostructures are thus important for application in transistors with improved current driving capabilities.Extended version of a paper presented at the18th Int. Symp. GaAs Related Compounds (Heraklion, Crete, 1987)     

Early stage ageing effects and shallow positron traps in Al–Mg–Si alloys

Room temperature ageing, so-called natural ageing, of Al–Mg–Si alloys has a subtle but striking influence on the mechanical properties achievable by subsequent ageing at more elevated temperatures. Though strongly debated, different clustering processes are generally accepted to give rise to this effect. Using temperature-dependent positron lifetime measurements of naturally aged Al–Mg–Si alloys, it is shown that in the early stages of ageing, small clusters of alloying atoms without embedded vacancies take part in the decomposition process. These clusters serve as shallow positron traps with a binding energy of about 55(10) meV, grow in the course of natural ageing and transform to deep positron traps with binding energies well above thermal energies. Thus, results of positron annihilation spectroscopy techniques need to be interpreted carefully with respect to the microstructure of age-hardenable Al alloys. Moreover, it is shown that a simple approach to bind positron states using a three-dimensional potential well and (bulk) positron affinities cannot explain the present findings.     

Bose–Einstein condensates in concentrically coupled annular traps with spin–orbit coupling and rotation

We investigate Bose–Einstein condensates in concentrically coupled annular traps with spin–orbit coupling and rotation. The ground state wave functions are computed by minimizing the Gross–Pitaevskii energy functional, and the combined effects of system?s parameters, especially the spin–orbit coupling and rotating, are investigated. The results show that for a finite fixed spin–orbit coupling, with increasing the angular frequency of rotation, the system is always in phase coexistence. Moreover, phase transitions between different ground state phases can be induced not only by spin–orbit coupling, but also rotation, which resembles very much the one where the s-wave interactions are varied.     

Experiments with single atoms in cavities and traps

ＥｘｐｅｒｉｍｅｎｔｓｗｉｔｈｓｉｎｇｌｅａｔｏｍｓｉｎｃａｖｉｔｉｅｓａｎｄｔｒａｐｓＨ．Ｗａｌｔｈｅｒ（ＳｅｋｔｉｏｎＰｈｙｓｉｋｄｅｒＵｎｉｖｅｒｓｉｔａｔＭｕｎｃｈｅｎａｎｄＭａｘ－Ｐｌａｎｃｋ－ＩｎｓｔｉｔｕｔｆｕｒＱｕａｎｔｅｎｏｐｔｉｋ...     

Synthesis and electrochemical characterization of nitrogen-doped and nitrogen–phosphorus-doped multi-walled carbon nanotubes

Nitrogen-doped and nitrogen–phosphorus-doped multi-walled carbon nanotubes (N-MWCNTs and N–P-MWCNTs, respectively) were fabricated by chemical vapor deposition and characterized using scanning electron microscopy and transmission electron microscopy in combination with energy dispersive X-ray spectroscopy and Raman spectroscopy. The electrochemical response of N-MWCNTs and N–P-MWCNTs towards ferrocyanide/ferricyanide was initially studied. The findings exhibit weakening of electrochemical response and sensitivity of nanotubes with phosphorus doping, and thus, within the composite films tested, those consist exclusively of N-MWCNTs exhibit the greatest electrocatalytic activity. N–P-MWCNT film was further applied for individual electrochemical analysis of ascorbic acid (AA), uric acid (UA), and dopamine (DA), and lower limits of detections of 11.6, 7.8, and 1.9 μM were estimated, respectively. The findings demonstrate that AA does not interfere with UA, but considerable interference of AA in analysis of DA was observed. Thus, the simultaneous analysis of AA, UA, and DA on N–P-MWCNTs appears to be restricted.     

Transient characteristics of the InGaP–GaAs–InGaAs–GaAs transistor laser

Transient characteristics of the InGaP–GaAs–InGaAs (quantum well)-GaAs transistor laser are studied. Rate equations are numerically solved to obtain the response of current density and photon density. Expression of resonance frequency $f_{r}$ is obtained by solving the rate equations analytically. It has been found that the $f_{r}$ increases with decreasing spontaneous carrier lifetime and with increasing value of the bias current density.     

Theoretical study of novel B–C–O compounds with non-diamond isoelectronic

Two novel non-isoelectronic with diamond(non-IED)B–C–O phases(tI16-B₈C₆O₂and mP16-B₈C₅O₃)have been unmasked.The research of the phonon scattering spectra and the independent elastic constants under ambient pressure(AP)and high pressure(HP)proves the stability of these non-IED B–C–O phases.Respective to the common compounds,the research of the formation enthalpies and the relationship with pressure of all non-IED B–C–O phases suggests that HP technology performed in the diamond anvil cell(DAC)or large volume press(LVP)is an important technology for synthesis.Both tI16-B₈C₆O₂and tI12-B₆C₄O₂possess electrical conductivity.mP16-B₈C₅O₃is a small bandgap semiconductor with a 0.530 eV gap.For aP13-B₆C₂O₅,mC20-B₂CO₂and tI18-B₄CO₄are all large gap semiconductors with gaps of 5.643 eV,6.113 eV,and 7.105 eV,respectively.The study on the relationship between band gap values and pressure of these six non-IED B–C–O phases states that tI16-B₈C₆O₂and tI12-B₆C₄O₂maintain electrical conductivity,mC20-B₂CO₂and tI18-B₄CO₄have good bandgap stability and are less affected by pressure.The stress-strain simulation reveals that the max strain and stress of 0.4 GPa and 141.9 GPa respectively,can be sustained by tI16-B₈C₆O₂.Studies on their mechanical properties shows that they all possess elasticity moduli and hard character.And pressure has an obvious effect on their mechanical properties,therein toughness of tI12-B₆C₄O₂,aP13-B₆C₂O₅,mC20-B₂CO₂and tI18-B4CO4 all increases,and hardness of mP16-B₈C₅O₃continue to strengthen during the compression.With abundant hardness characteristics and tunable band gaps,extensive attention will be focused on the scientific research of non-IED B–C–O compounds.     

Control of circular polarization of electroluminescence in spin light-emitting diodes based on InGaAs/GaAs/δ〈Mn〉 heterostructures

Circularly polarized luminescence of light-emitting InGaAs/GaAs structures with a delta-doped Mn layer in a GaAs barrier was studied. The structural parameters were varied by different ways, among them are homogeneous and delta-doping with acceptor impurity, and removal of donor doping from the technological process. As it was found, the magnitude and polarity of the degree of circular polarization of luminescence strongly depend on the technological mode chosen. Simultaneous modeling of wave functions of structures highlights a good agreement between the parameters of circularly polarized luminescence and spatial distribution of wave functions of heavy holes relative to the Mn delta-layer.     

Effect of NO annealing on charge traps in oxide insulator and transition layer for 4H-SiC metal–oxide–semiconductor devices

The effect of nitric oxide(NO) annealing on charge traps in the oxide insulator and transition layer in n-type4H–Si C metal–oxide–semiconductor(MOS) devices has been investigated using the time-dependent bias stress(TDBS),capacitance–voltage(C–V),and secondary ion mass spectroscopy(SIMS).It is revealed that two main categories of charge traps,near interface oxide traps(Nniot) and oxide traps(Not),have different responses to the TDBS and C–V characteristics in NO-annealed and Ar-annealed samples.The Nniotare mainly responsible for the hysteresis occurring in the bidirectional C–V characteristics,which are very close to the semiconductor interface and can readily exchange charges with the inner semiconductor.However,Not is mainly responsible for the TDBS induced C–V shifts.Electrons tunneling into the Not are hardly released quickly when suffering TDBS,resulting in the problem of the threshold voltage stability.Compared with the Ar-annealed sample,Nniotcan be significantly suppressed by the NO annealing,but there is little improvement of Not.SIMS results demonstrate that the Nniotare distributed within the transition layer,which correlated with the existence of the excess silicon.During the NO annealing process,the excess Si atoms incorporate into nitrogen in the transition layer,allowing better relaxation of the interface strain and effectively reducing the width of the transition layer and the density of Nniot.     

Thermal conductivity of nitrogen in the temperature range 350–2500 K

The thermal conductivity of nitrogen is determined in a conductivity column instrument in the temperature range of 338 to 2518 K with an estimated uncertainty of about ± 1·5 per cent. The experimental data points are correlated by a cubic polynomial in temperature, viz. k(T)/(mW m^-1 K^-1) = 12·18 + 0·05224(T/K) - 0·6482 × 10^-6(T/K)² - 0·2765 × 10^-9(T/K)³. These conductivity values determined from heat transfer data taken in the continuum regime are found to be in fair agreement with the values obtained from similar data referring to low pressure range.

The present results are compared with the conductivity determinations of other workers and with the predictions of various theories developed for polyatomic gases. It is pointed out that a reliable calculation of thermal conductivity over an extended temperature range is impossible at the present time due to the absence of a large variety of experimental molecular data needed for such an effort. Average values of the vibrational energy diffusion coefficient, D _vib, are computed from the present k(T) data.     

Near-interface oxide traps in 4H–SiC MOS structures fabricated with and without annealing in NO

Near-interface oxide traps(NIOTs)in 4H–Si C metal–oxide–semiconductor(MOS)structures fabricated with and without annealing in NO are systematically investigated in this paper.The properties of NIOTs in Si C MOS structures prepared with and without annealing in NO are studied and compared in detail.Two main categories of the NIOTs,the"slow"and"fast"NIOTs,are revealed and extracted.The densities of the"fast"NIOTs are determined to be 0.76×10~(11)cm~(-2)and0.47×10~(11)cm~(-2)for the N_2 post oxidation annealing(POA)sample and NO POA sample,respectively.The densities of"slow"NIOTs are 0.79×10~(11)cm~(-2)and 9.44×10~(11)cm~(-2)for the NO POA sample and N_2POA sample,respectively.It is found that the NO POA process only can significantly reduce"slow"NIOTs.However,it has a little effect on"fast"NIOTs.The negative and positive constant voltage stresses(CVS)reveal that electrons captured by those"slow"NIOTs and bulk oxide traps(BOTs)are hardly emitted by the constant voltage stress.     

Thermally stimulated terahertz radiation of plasmon–phonon polaritons in GaAs

The thermally stimulated excitation of radiative modes of surface plasmon–phonon polaritons in GaAs followed by the high-power terahertz (THz) radiation selective emission is studied and experimentally observed. The selective high-power THz radiation emitters in the 7–8 and 10–15 THz frequency ranges based on the heated highly doped (n>5?10¹⁷ cm^?3) GaAs plates are proposed.     

Growth and Characterization of GaAs／A1GaAs Thue-Morse Quasicrystal Photonic Bandgap Structures

One-dimensional quasicrystal structures composed of Ⅲ-Ⅴ semiconductor GaAs/AlGaAs multilayers in deterministic Thue-Morse (TM) sequences have been grown by using gas-source molecular beam epitaxy to investigate both the structural and the photonic bandgap properties. The x-ray measurements show that this aperiodic system exhibits obvious periodic spatial correlations, from which the precise thickness of the constitutive layers could be determined. Transmission and reflection measurements experimentally demonstrated plenty of photonic bandgaps with traditional or fractal features existing in those quasicrystal structures, which are in good agreement with the transfer matrix simulations. The diversity of this TM system makes it a good candidate for photonic device applications.     

Fabrication of particular structures of hexagonal boron nitride and boron–carbon–nitrogen layers by anisotropic etching

Anisotropic etching of hexagonal boron nitride (h-BN) and boron–carbon–nitrogen (BCN) basal plane can be an exciting platform to develop well-defined structures with interesting properties. Here, we developed an etching process of atomically thin h-BN and BCN layers to fabricate nanoribbons (NRs) and other distinct structures by annealing in H₂ and Ar gas mixture. BCN and h-BN films are grown on Cu foil by chemical vapor deposition (CVD) using solid camphor and ammonia borane as carbon, nitrogen and boron source, respectively. Formation of micron size well-defined etched holes and NRs are obtained in both h-BN and BCN layers by the post growth annealing process. The etching process of h-BN and BCN basal plane to fabricate NRs and other structures with pronounced edges can open up new possibilities in 2D hybrid materials.     

Photo-acoustic spectrum and detection of nitrogen dioxide

The photo-acoustic (PA) spectrum of nitrogen dioxide (NO2) in the range of 420 - 520 nm with a Nd:YAG pumped optical parametric generator and amplifier as radiation source is presented. The spectrum has a characteristic of banded structure superimposed on continuum. The banded structure of the spectrum can be assigned to NO2 B2B1 ←X2A1 transition. While the continual one comes from the chaos states of the first excited state A2B2 and the high vibration levels of the ground state X2A1. The relationship of PA signal with buffer gas pressure and NO2 concentration is measured. The PA signal intensity increases with buffer gas pressure and almost is invariable when the buffer gas pressure is more than 3.00×104 Pa. The PA signal intensity has linearity with NO2 concentration. The detection limit is about 2×10-5 on the basis of SNR = 1, however lower value of the detection limit can be expected by improving the apparatus properties.