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A detailed study is reported of Si spreading in slab- and delta-doped In0.53Ga0.47As grown lattice matched to InP substrates by molecular beam epitaxy at temperatures from approximate to 420 to approximate to 520 degrees C and doping concentrations From 2 X 10(12) to 1.5 X 10(13) cm(-2). The spreading is deduced by comparing the individual subband densities calculated from a fast Fourier transform analysis of Shubnikov-de Haas measurements with those derived from self-consistent calculations for which the doping profile width is used as a fitting parameter. The growth conditions for the epitaxial layers were designed to differentiate between surface segregation and thermal diffusion of the dopant atoms. Surface segregation is found to be the dominant mechanism causing Si spreading at growth temperatures higher than approximate to 470 degrees C. An ideal S-doping profile in In0.53Ga0.47As requires only the growth of a thin cap layer of undoped material at temperatures less than approximate to 470 degrees C over the delta doping. Holding the substrate temperature at values up to approximate to 520 degrees C during delta doping or the subsequent deposition of material over the cap does not produce any spreading. The three-band Kane model is found to provide an adequate description of the electronic properties of narrow Si doping profiles with carrier concentrations as high as 1.5 X 10(13) cm(-2) and Fermi energies close to 550 meV, the separation between the Gamma- and L-conduction band minima in In0.53Ga0.47As. The free electron concentrations from low magnetic field Hall measurements are consistently less than the sums of the individual subband densities derived from the Shubnikov-de Haas effect. In addition, for the same total Si doping density, the apparent electron concentration from Hall measurements is lower when the Si dopants are more confined compared with the case where the dopants are significantly spread. These apparent discrepancies are shown to follow from the different subband mobilities expected in these structures. From the data a direct measure of the standard deviation of carrier mobilities over subbands for a given structure is obtained. [S0163-1829(99)04515-4]. Physical Review B

We have measured the magnitude of the potential modulation below gated one-dimensional lateral surface superlattices fabricated with periods between 60 and 600 nm on a range of GaAs/AlGaAs heterostructures. The magnitude of the modulation was obtained by studying the amplitude of the commensurability oscillations in magnetoresistance, and confirmed by analysis of the low field positive magnetoresistance step. Without gate bias applied, the modulation is generated by strain in Che gates, coupled piezoelectrically to the two-dimensional electron gas. Both magnitude and harmonic content of the potential are in reasonable agreement with a recent theoretical calculation of this coupling, over the full range of periods and for all the structures studied. Away from zero gate bias electrostatic modulation adds to the piezoelectric component. This differs according to the sign of the applied bias. In depletion it increases roughly linearly with-bias and is in good agreement with theoretical estimates, whereas in positive bias it tends to saturate as strong screening in the donor layers develops. Physical Review B

Magnetotransport measurements are reported for In0.53Ga0.47As layers grown by molecular beam epitaxy (MBE) at different substrate temperatures (T-s) and either delta or slab-doped with Si. Multiple subband densities deduced from the Fourier analysis of 1.2 K Shubnikov-de Haas measurements are compared with those derived from self-consistent calculations which include nonparabolicity and the doping profile width w(Si) as a fitting parameter. Significant spreading of the Si donors away from the doping plane is deduced for deposition at T-s approximate to 520 degrees C, while no measurable migration is inferred for T-s less than or equal to 470 degrees C, leading to near-ideal delta-doping behavior. Contrary to previous results [McElhinney et al., J. Cryst. Growth 150, 266 (1995)], no evidence for amphoteric behavior has been found for Si areal densities up to 4 X 10(12) cm(-2). (C) 1996 American Institute of Physics. Applied Physics Letters

Two series of shallow GaAs heterostructures, with AlGaAs and AlAs barriers respectively and both delta-doped with around 4 x 10(16) m(-2) Si donors, have been studied using low-temperature magnetotransport techniques. The electrons in these structures were confined against interfaces 28 nm from the surface. The AlGaAs barrier samples depleted at a uniform rate with bias under a Schottky gate, but the carrier mobility was considerably greater at all biases than predicted assuming randomly positioned donors. The depletion and mobility data for the AlAs barrier samples could only be explained by postulating the existence of a pool of electrons around the doping plane, which screened the donors to produce high mobilities in ungated samples but which could be removed by the application of gate bias. Bias cooling experiments on the AlGaAs samples showed that a proportion of the donor centres were occupied when samples with as few as 4 x 10(16) m(-2) donors were cooled without bias. The mobility data from such samples are discussed assuming correlations between the positions of these occupied donors. Semiconductor Science and Technology

A series of two-dimensional electron gas (2DEG) structures have been grown with the 2DEG only 28 nm from the surface. The effects of growth temperature and delta-doping density have been investigated, and a comparison has been made between AlAs and Al0.3Ga0.7As barriers. A mobility of 330,000 cm(2) V-1 s(-1) at 4 K has been measured for a shallow 2DEG with an Al0.3Ga0.7As barrier, which is the highest reported for such a structure. Journal of Crystal Growth