Si diffusion in GaAs

Theoretical studies are carried out to ascertain the dominant mechanism of Si diffusion in GaAs. Lattice dynamical model calculations have shown that the most probable diffusion mechanism is through a single vacancy even though several experiments cannot fix the mechanism as substitutional, substitutional-interstitial pair or neutral defect pair.     

Anomalous diffusion profiles of zinc in GaAs

A number of workers investigating diffusion in semiconductors using radio-tracer techniques have reported a type of profile which is not easily explained by current theories of diffusion. This anomalous profile is usually found in experiments in which the solute concentration is high and has often been associated with the substitutional-interstitial diffusion mechanism. The profile shape is considered in this paper, taking the diffusion of zinc in GaAs at 1000° C as an example. The use of the Boltzman-Matano technique for analysing complex diffusion profiles is considered and experiments are described which suggest that the technique is not appropriate for this type of profile. An adaptation of the substitutional-interstitial diffusion theory is presented in which allowance is made for the possibility of the gallium vacancy concentration falling below the thermal equilibrium value. Theoretical profiles are computed and compared to experiments. Reasonable agreement is found.     

The growth of high purity GaAs by molecular beam epitaxy in diffusion pumped system

Diffusion pumped MBE systems are likely to be technologically important in the development of production semiconductor growth equipment. It is demonstrated, for the first time, that high quality GaAs can be produced in such systems. Both electrical and optical results are presented to illustrate these findings.     

Solid-phase diffusion mechanism for GaAs nanowire growth

Controllable production of nanometre-sized structures is an important field of research, and synthesis of one-dimensional objects, such as nanowires, is a rapidly expanding area with numerous applications, for example, in electronics, photonics, biology and medicine. Nanoscale electronic devices created inside nanowires, such as p-n junctions, were reported ten years ago. More recently, hetero-structure devices with clear quantum-mechanical behaviour have been reported, for example the double-barrier resonant tunnelling diode and the single-electron transistor. The generally accepted theory of semiconductor nanowire growth is the vapour-liquid-solid (VLS) growth mechanism, based on growth from a liquid metal seed particle. In this letter we suggest the existence of a growth regime quite different from VLS. We show that this new growth regime is based on a solid-phase diffusion mechanism of a single component through a gold seed particle, as shown by in situ heating experiments of GaAs nanowires in a transmission electron microscope, and supported by highly resolved chemical analysis and finite element calculations of the mass transport and composition profiles.     

Doppler-enhanced gain in an open ladder inversionless lasing system

Abstract

An analysis is made of the effect of Doppler broadening on the gain in an open ladder inversionless lasing system. It is shown that for co-propagating probe and driving fields, the gain does not monotonously decrease or increase with increasing Doppler width, and at a suitable Doppler width one can obtain a maximum value much larger than that without Doppler broadening. For counterpropagating probe and driving fields, when the Doppler width is large enough, gain oscillation occurs, and the oscillation amplitude and region increase with increasing Doppler width. This conclusion is very different from that obtained in the corresponding closed system.     

Optical bistability and multistability in an open ladder-type atomic system

A novel scheme is proposed for controlling the optical bistability and multistability in an atomic system. In an open ladder-type three-level atomic system, it is shown that, by adjusting the ratio between atomic injections and exit rates from the cavity, the intensity threshold of optical bistability can be controlled. The effect of incoherent pumping field and spontaneously generated coherence (SGC) on optical bistability for different values of exit rates is also discussed. It is found that SGC makes the medium phase dependent, so the optical bistability and multistability threshold can be controlled via relative phase between applied fields. Moreover, it is shown that the optical bistability can be switched to optical multistability, which is favorable for the next generation of all-optical systems and quantum networks.     

Isoconcentration diffusion of zinc in GaAs at 1000° C

A series of experiments is described in which zinc is diffused into GaAs at 1000° C using an isoconcentration technique. Standard error function complement profiles are obtained and graphs are produced showing the variation of diffusion coefficient with zinc concentration. Work carried out at two different arsenic vapour pressures is described and the effect of a variation in the stoichiometry of the semiconductor is thereby examined. The results of both sets of experiments are shown to agree with a substitutional-interstitial mechanism for the diffusion of zinc in GaAs. The solubility of zinc in GaAs is investigated as a function of ambient zinc vapour pressure and arsenic pressure. The results agree with a simple interpretation of the zinc as an almost completely ionised acceptor. A value is calculated for the maximum attainable solubility at 1000°C for GaAs in equilibrium with zinc vapour.     

Investigation of indium diffusion process in In ion implanted GaAs

Rutherford backscattering (RBS) has been used to determine diffusion coefficients of indium atoms in semi-insulating (1 0 0) GaAs implanted with 250 keV In⁺ ions at a fluence of 3×10¹⁶ cm⁻² and isobarically annealed at 600 and 800 °C temperature. Computer modeling of the indium depth profiles based on Ga vacancy-mediated diffusion has shown good agreement with the RBS experimental results. Self-annealing effect was confirmed to play an important role due to high defect mobility at room temperature ion implantation. Large values of the In diffusion coefficients obtained in the present study, in comparison with the literature data for unimplanted GaAs, confirms strong enhancement of the diffusion process by radiation damage.     

Phase control of gain and dispersion in an open V-type system

The control role of the relative phase between the probe and driving fields on gain, dispersion and populations in an open V-type three-level system with spontaneously generated coherence is studied. The result shows that by adjusting the value of the relative phase, the transformation between lasing with inversion and lasing without inversion (LWI) can be realized and high dispersion (refractive index) without absorption can be obtained. The shape and value range of the dispersion curve are similar to those of the gain curve, and this similarity is closely related to the relative phase. The effects of the atomic exit and injection rates and the incoherent pump rate on the control role of the relative phase are also analysed. It is found easier to get LWI by adjusting the value of the relative phase using the open system rather than the closed system, and using an incoherent pump rather than without using the incoherent pump. Moreover the open system can give a larger LWI gain than the closed system.     

Group velocity of probe light pulse in an open lambda system

The group velocity of the probe light pulse (GVPLP) propagating through an open Λ-type atomic system with a spontaneously generated coherence is investigated when the weak probe and strong driving light fields have different frequencies. It is found that adjusting the detuning or Rabi frequency of the probe light field can realize switching of the GVPLP from subluminal to superluminal. Changing the relative phase between the probe and driving light fields or atomic exit and injection rates can lead to GVPLP varying in a wider range, but cannot induce transformation of the property of the GVPLP. The absolute value of the GVPLP always increases with Rabi frequency of the driving light field increasing. For subluminal and superluminal propagation, the system always exhibits the probe absorption, and GVPLP is mainly determined by the slope of the steep dispersion.     

Stable ohmic contact to GaAs with TiN diffusion barrier

Ti/TiN/Ag ohmic contacts to p-type GaAs were studied. The contacts were formed by a solid phase reaction between titanium and GaAs. The interposed TiN film acts as an excellent diffusion barrier in two respects. It confines the reactions between titanium and GaAs, and it prevents the intermixing of the top silver layer with titanium and GaAs below. The contact resistivity of this metallization system is stable up to 500°C for 2 h.     

扩散真空泵性能自动测试系统的研制

本文介绍了一套新研制的扩散真空泵件能的自动测试系统.该系统可以按照国家标准规定的方法自动检测扩散真空泵的极限压力和抽速.系统利用自主开发的光电液位检测方法和元件实现滴管液位的自动读取和记时;利用步进电机驱动针阀实现气体流量和测试罩内压力的自动调节;使用上位PC机和下位单片机的双级控制系统实现对整个测试系统和测试过程的自动控制.     

Effects of gold diffusion on n-type doping of GaAs nanowires

The deposition of n-GaAs shells is explored as a method of n-type doping in GaAs nanowires grown by the Au-mediated metal-organic chemical vapor deposition. Core-shell GaAs/n-GaAs nanowires exhibit an unintended rectifying behavior that is attributed to the Au diffusion during the shell deposition based on studies using energy dispersive X-ray spectroscopy, current-voltage, capacitance-voltage, and Kelvin probe force measurements. Removing the gold prior to n-type shell deposition results in the realization of n-type GaAs nanowires without rectification. We directly correlate the presence of gold impurities to nanowire electrical properties and provide an insight into the role of seed particles on the properties of nanowires and nanowire heterostructures.     

Shallow diffusion of zinc into GaAs for optical waveguide modulators

We developed a diffusion technique for the fabrication of a coupled-waveguide optical modulator with a p-n junction in a strip-loaded channel-waveguide configuration. Zinc was diffused into n-type GaAs at 580°C for 2 h in a closed tube. The diffused p⁺ layer was as thin as 1.3 μm, and the stepwise diffusion profile was explained using the theory of substitutional-interstitial diffusion. The modulator was formed by chemical etching on an n/n⁺-GaAs wafer prepared by vapour phase epitaxy with subsequent diffusion of the p⁺ surface layer.     

An open distributed measurement system based on an abstract client-server architecture

This paper describes in detail a Java-based, client-server architecture specifically designed to allow a flexible management of remote instruments. The main attributes of the proposed solution are portability and extensibility. The former feature is assured by the employment of the TCP/IP protocol suite and by the Java language properties. The latter is due to the high level of abstraction of the system implementation. This approach addresses a wide range of possible applications with high code reusability. In fact, the proposed architecture permits to drive many kinds of different devices and can be easily upgraded simply by adding a limited amount of code on the server computer whenever a new instrument is connected to the system.     

Buffer-gas-induced narrowing of electromagnetically induced transparent spectra for an open system

We have investigated the spectra of the electromagnetically induced transparency (EIT) when a cell is filled with a buffer gas. Our theoretical results show that the buffer gas can induce a narrower spectra line and steeper dispersion than those of the usual EIT case in a homogeneous and Doppler broadened system. The linewidth decreases with the increase of the buffer gas pressure. This narrow spectra may be applied to quantum information processing, nonlinear optics and atomic frequency standard.     

Gas-phase transport phenomena at low temperatures: Thermal diffusion in an Ar-Kr system

A metal two-bulb apparatus for the measurement of the thermal diffusion factor, _T , especially at temperatures below room temperature, has been designed and constructed. The results for the argon-krypton system are reported, and these cover five mixture compositions (25, 40, 50, 60, and 75% of krypton). The top bulb is maintained at 293.2 K, while the temperature of the lower bulb is varied in the range 102–250 K. The measured _T values are estimated to be accurate within ±4%. The positive minimum in the present _T values is less pronounced than that reported by some other workers, and this is attributed to the operating conditions and to the apparatus geometry.     

Phase control of gain and dispersion in an open lambda-type inversionless lasing system

The control role of the relative phase between the probe and driving fields on the gain and dispersion in an open Λ-type inversionless lasing system with spontaneously generated coherence (SGC) is investigated. It is shown that the inversionless gain and dispersion are quite sensitive to variation in the relative phase; by adjusting the value of the relative phase, electromagnetically induced transparency (EIT), a high refractive index with zero absorption and a larger inversionless gain can be realized. It is also shown that, in the contributions to the inversionless gain (absorption) and dispersion, the contribution from SGC is always much larger than that from the dynamically induced coherence for any value of the relative phase. Our analysis shows that variation in the SGC effect will cause the spectrum regions and values of the inversionless gain and dispersion to vary evidently. We also found that, under the same conditions, the values of the inversionless gain and dispersion in the open system are evidently larger than those in the corresponding closed system; EIT occurs in the open system but cannot occur in the closed system.