Carbon Doping in InGaAs grown by MBE
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CARBON DOPING IN InGaAs GROWN BY MBE HIROSHI ITO AND TADAO ISHIBASHI NTT LSI Laboratories, 3-1, Morinosato Wakamiya, JAPAN
Atsugi-shi,
Kanagawa 243-01
ABSTRACT Carbon doping in InxGailxAs is investigated using solid source MBE. InAs mole fractions, x, from 0 to 1 are tested. Under a constant doping level, hole concentration decreases with increasing x. When x is higher than 0.6, the conduction type is n and electron concentration increases with x. The conduction-type inversion and the behavior of carrier mobilities are explained by a self-compensation mechanism.
INTRODUCTION Heavily doped semiconductor layers are very important in fabricating various high-speed electron and optoelectronic devices because extremely low contact and sheet resistances are generally required. Be [13 and Zn (2] are widely used as p-type dopants in MBE and MOCVD growth of III-V compound semiconductors since very high carrier concentrations of required levels can be obtained with them. However, diffusion coefficients of these dopants are not sufficiently small (1,3) at the temperatures generally used for epitaxial growth of various devices. Recently, C has gained popularity as a p-type dopant for GaAs. Its diffusion coefficients in GaAs crystals are 1- 2 orders of magnitude smaller than those of Be or Zn. Its maximum available free carrier concentration of 3 1.5 x 1021 cm[41 is also higher than that of Be or Zn. InGaAs layers are promising materials for future high speed devices due to high electron mobility and high peak electron drift velocity. Thus, carbon doping for In 0 . 5 3 Ga0 . 4 7 As lattice matched to InP substrate is of great interest. Only two experiments on C doping for InGaAs have been reported to date. One is by the MOMBE method using metal alkyls as C sources [5]. All the C doped InGaAs layers obtained were n-type, regardless of source material. The other experiment was by the MOCVD method using CCI 4 as the C source, which resulted in p-type InGaAs layers [6]. In the former case, C impurities were highly compensated in InGaAs, which indicated the amphoteric characteristics of C in the (In,Ga)As system at a In mole fraction of 0.53. This paper reports C doping for InGaAs by solid source MBE. Indium mole fractions in the (In,Ga)As system from 0 (GaAs) to 1 (InAs) were tested.
EXPERIMENTAL The MBE system used in this study was the RIBER 2300P. Epi-layers were grown directly on (100) oriented semi-insulating GaAs substrates. A graphite filament [7] , heated by flowing current directly through the filament, was used as the C source. The growth rate was I pm/h, and the V/III ratio was about 5. Substrate temperatures from 400'C (InAs) to 650°C Mat. Res. Soc. Symp. Proc. Vol. 163.
1990 Materials Research Society
888
(GaAs) were used for The mole fraction. were grown layers temperature of the C
the growth, selecting the appropriate value for each In free carrier concentration and Hall mobility of the The evaluated using van der Pauw measurements. filament was measured with an optical pyrometer.
RESULTS AND DISCUSSION Th
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