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The conductance of a narro~two-dimensional electron gas in a GaAs:AlQ3GaQ7As heterojunction fluctuates as a function of magnetic field. The variance and correlation length of the fluctuations have been measured for a number of temperatures, and the electron phase-breaking length is found to vary as a small negative power of the temperature. e2 LTWhen the temperature is reduced to a value such that L& and LT are larger than L, the amplitude of the fluctuations saturates at a value given by Eq. (1).The fluctuations in the conductance are correlated in the magnetic field and it is useful to calculate the correlation function F(8,/JB) =(g(8)g(8+/JB)) -(g (8)) . For hB =0 the correlation function reduces to the variance (d, g ). For an arbitrary AB the correlation function F(B,AB) can be characterized by a magnetic correlation length 8, such that F(B,B,)/F(B, O) = -, '. In a quasi-The observation that small, normal-metal wires and rings exhibit reproducible, aperiodic, oscillations in the magnetoconductance' has prompted a number of theoretical and experimental " studies of small systems. It is now clear that the conductance fluctuations are universal in the sense that at T=O the root-mean-square (rms) deviation from the mean (Ag )'~i s approximately e /h regardless of sample size and degree of disorder, i.e. , (gg2)1/2((gg2)(gg)2)~e2/h The angle brackets denote ensemble averaging and 6g =g(EF, B) -(g(FF, B)). The constant a depends upon the shape of the sample and is of the order of unity but should be calculated numerically for the particular geometry being considered. For a quasi-one-dimensional wire (W&&L&) a=0.729 (Refs. 4 and 7) and this is the value that will be used here. At finite temperatures the temperature dependence of the fluctuations takes on a number of diA'erent forms depending upon the relative sizes of the interaction length LT = (hD/ke T) ', the phase coherence length L&, and the device length L. In one dimension, when 8' & L&,LT, the rms amplitude of the fluctuations is given by one-dimensional sample it is given by 1.2gp/(WL~), L~& L 12~~L. L&L. ,where D is the diffusion coe%cient and g is the Boltzmann conductance. In the paper we present results on the universal conductance fluctuations of a narrow 2D EG. The variance and correlation function of the fluctuations have been measured at diferent temperatures and used to determine the temperature dependence of L&. The devices were split-gate heterojunction field-eA'ect transistors (FET's) with a gate separation of 1 pm, length 15 pm, and have been discussed elsewhere. ' ' The 2DEG under the gates can be removed by a negative gate voltage leaving only a narrow channel between the gates. Progressively reverse biasing the gates reduces the width of the channel until it is eventually removed by a gate voltage of -3.5 V. Low-field magnetoconductance measurements were carried out below 4.2 K, where it was necessary to use source-drain fields of less than 1 Vm to prevent electron heating. The fluctuations in the conductance of a channel defined by a gate ...

The direct energy gap of thin, undoped epitaxial layers of Al1−xInxAs grown on (100) InP has been measured as a function of In content for values of x between 0.46 and 0.55 using catholuminescence spectroscopy. For the composition lattice matched to InP it was measured to be 1.450 eV at room temperature, and 1.508 eV at 4 K. Over the limited range of compositions studied, it varied as Eg =1.450+2.29 Δx eV at room temperature, and as Eg =1.508+2.22 Δx eV at 4 K, where Δx=(0.52−x), the deviation of x from the lattice-matched value.

The adsorption of triethylgallium on the GaAs (100) (4×1) surface has been studied using the techniques of low energy electron diffraction, x-ray photoelectron and Auger spectroscopies, high resolution electron energy loss spectroscopy and temperature-programmed desorption. Condensed multilayers of the organometallic compound formed following adsorption at 150 K desorb from the surface at ∼170 K to leave a chemisorbed molecular monolayer of triethylgallium. Upon further heating this layer partially desorbs and partially decomposes to form diethylgallium in two competing processes. The diethylgallium so formed can also desorb or otherwise decompose ultimately to adsorbed Ga atoms in a reaction which results in the formation of hydrogen, ethene, and ethane. The temperature-programmed desorption characteristics of these latter species are found to be similar to those observed for a dissociated layer of ethyl bromide. A reaction scheme is proposed to account for the observations and kinetic parameters are obtained from computer modeling of the temperature-programmed desorption results. The reaction scheme is also used to evaluate the temperature-dependent growth rate expected in metal organic molecular beam epitaxial growth of GaAs. Comparison with experimental results is made and the work is discussed in the light of the previous model which has been proposed for the epitaxial growth of GaAs by metal organic molecular-beam epitaxy.

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