Effects of Carbon-Ion Irradiation-Energies on the Molecular Beam Epitaxy of GaAs and Ingaas
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Abstract Carbon ion (C') irradiation during molecular beam epitaxy (MBE) growth of GaAs/GaAs and In0 53Ga 047As/InP layers was carried out using CIBMBE (combined ion beam and molecular beam epitaxy) method as a function of wide acceleration energy (E,=30 eV-30 keV) at a constant ion beam current density. Judging from the monitored current density and the net hole concentration (INA-NDI) obtained from Hall effect measurements, activation rate as high as 88% was achieved for as-grown GaAs layers by C' ion irradiation of E,=- 170eV. It was revealed that by annealing at 800'C, a slight enhancement (-10%) of INA-NDI is practiced for Ea- lkeV. In In0 s3Ga 047As/InP layers with increasing E., a type conversion of electric conduction from n to p was found to occur at E,= -70-100eV. These observations describe that Ea plays a vital role to determine the location of incorporated electrical and optical active impurities in GaAs and InGaAs. Further for comparison, C'-implanted GaAs layers were prepared by high-energy (400 keV) ion-implantation as a function of substrate temperature (T,=RT600 °C). For C dose concentration of lxlIO'cm3 , the highest activation rate of -20 % was obtained at T,=-150 0 C. This result states that CIBMBE method is a superior doping method in view of activation rate of introduced dopants and the formation of damage-free ion-irradiated layers. 1. Introduction The advantage of ion-beam doping technique is the high controllability of important doping parameters such as dopant species (high mass purity) and concentration. Since this method is a thermally non-equilibrium technique, the above parameters are independent of growth conditions of host materials such as growth temperature for the case of molecular beam epitaxy (MBE). In
a) On leave from Chiba University, 1-33 Yayoi-cho, Inage, Chiba, Chiba 263, Japan. b) On leave from Tokai University, 1117 Kitakaname, Hiratsuka 259-12, Japan. 241 Mat. Res. Soc. Symp. Proc. Vol. 388 0 1995 Materials Research Society
solid-source MBE system, evaporation of dopant material using effusion cell is a most commonly used doping method. If the growth chamber is properly designed, the accidental incorporation of undesired impurities is normally governed by the purity of source materials. The decomposition and evaporation of crucible and heater materials are also other sources of contamination. In solidsource MBE, the doping efficiency and the dynamic range of dopant concentration are mainly determined by growth temperature, sticking coefficient and available vapor pressure. Accordingly except Si and Be, doping with a wide dynamic range of impurity concentration (10"' - 10"°cm') is usually very difficult to be achieved. High-energy ion implantation (HE-I2 ) is one of the most frequently used ion-beam doping technologies. Two main drawbacks about HE-I2 are the uneliminated radiation damage and the low activation rate even after suitable high-temperature annealing. The use of low-energy ion-beam (LE-IB) is one of the practical methods to minimize radiation damage [1-5].
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