Narrow Si doping distributions in 6-doped GaAs, Al 0.3 Ga 0.7 As and Quantum Wells grown by Gas Source Molecular Beam Ep
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Narrow Si doping distributions in 6-doped GaAs, Al 0.3 Ga 0.7As and Quantum Wells grown by Gas Source Molecular Beam Epitaxy J.E. Cunningham, T.H. Chin, B. Tell, W. Jan and J. A.Ditzenberger AT&T Bell Laboratories, Holmdel, NJ.,07733 and
T. Y.Kuo and C. Fonstad Massachusetts Institute of Technology, Cambridge, Mass.,02139 We report very small interdiffusion and surface segregation of Si in 6-doped GaAs, A10 .3Gao.TAs and Quantum Wells grown at 580 C by Gas Source Molecular Beam Epitaxy. Capacitance-Voltage profiles of 6-doped layers are 38 A wide for growth at 580 C and further, insignificant profile narrowing is observed at 530C and below. Much wider profiles are observed at equivalent substrate temperature for As 4 growth. Atomic diffusion of Si in 6-doped Alo.3 Gao.7As is found to have a rate of D, =5x l(V7 cm 2 /sec with an activation energy of 1.8 eV. L Introduction Recently, increasing interest in planar confinement of Si 6-doping impurities in the GaAs system have been stimulated by the introduction of new structures such as the 6-doped heterostructure [1,2,3] and the sawtooth 6-doping superlattice [4]. In these structures planar localization of the doping impurities is a necessary requirement to realize the full potential of the new concept. Early efforts to 6- dope GaAs with Si produced only quasi, two dimensional doping- distributions (100 A) when grown by Molecular Beam Epitaxy (MBE) at temperatures where the electrical properties of GaAs were optimized [5,6]. However, our preliminary results showed the doping profiles could be localized at 560C for Gas Source Molecular Beam Epitaxy (GSMBE) growth using AsH 3 [7,8]. More recently, it has become possible to produce 6-doped GaAs in which spatial spreading of Si is not observed by SIMS for structures grown below 500C by MBE methods [9]. Nevertheless, an important advantage of achieving spatial confinement of dopants at high growth temperatures is that a match can occur with the optimum temperatures required for good GaAs growth [10]. To further explore the difference in the localization characteristics of the 6-doping process using As 4 and AsH 3 , we spatially as well as the electrically profile the doping distributions by Capacitance-Voltage (C-V) techniques for each case. In addition, we have measured Si diffusion in 6-doped Alo.3 Gao.7As grown by GSMBE. We apply the results found from these measurements to determine electron mobility limitations observed in our previously reported 6-doped quantum well structure [111. 2 Results It has recently become known that differences in GaAs crystalline defect densities, photoluminescence response and doping efficiencies are related to growth using either AS 4 or AS2 . To determine if differences also accompany the electronic properties of the 6- doping profile for AsH 3 and As 4 growth ,we have measured the resultant C-V response of Si 6-doped GaAs versus growth temperature for each case. We employ for C-V measurement a layer structure consisting of a one micron buffer layer doped to lx 1018cm 3 grown on an n-typ
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