Si spreading in lattice-matched In0.53Ga0.47As grown by molecular-beam epitaxy

A detailed study is reported of Si spreading in slab- and delta-doped In0.5 3Ga0.47As grown lattice matched to InP substrates by molecular beam epitaxy at temperatures from approximate to 420 to approximate to 520 degrees C an d doping concentrations From 2 X 10(12) to 1.5 X 10(13) cm(-2). The spreadi ng is deduced by comparing the individual subband densities calculated from a fast Fourier transform analysis of Shubnikov-de Haas measurements with t hose derived from self-consistent calculations for which the doping profile width is used as a fitting parameter. The growth conditions for the epitax ial layers were designed to differentiate between surface segregation and t hermal diffusion of the dopant atoms. Surface segregation is found to be th e dominant mechanism causing Si spreading at growth temperatures higher tha n 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 temper atures less than approximate to 470 degrees C over the delta doping. Holdin g the substrate temperature at values up to approximate to 520 degrees C du ring delta doping or the subsequent deposition of material over the cap doe s not produce any spreading. The three-band Kane model is found to provide an adequate description of the electronic properties of narrow Si doping pr ofiles 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-conduct ion band minima in In0.53Ga0.47As. The free electron concentrations from lo w magnetic field Hall measurements are consistently less than the sums of t he individual subband densities derived from the Shubnikov-de Haas effect. In addition, for the same total Si doping density, the apparent electron co ncentration from Hall measurements is lower when the Si dopants are more co nfined compared with the case where the dopants are significantly spread. T hese 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 stru cture is obtained. [S0163-1829(99)04515-4].