Be diffusion in InGaAs epitaxial layers during rapid thermal annealing: an effective diffusivity approach and a nonequilibrium model

Abstract

Be diffusion during post-growth annealing has been studied in InGaAs epitaxial layers. To explain the observed concentration profiles, two models have been proposed. A good agreement has been obtained between experimental and calculated data. The point defect concentration in epitaxial layers during diffusion in InGaAs is also discussed. A-IntroductionA high p-type base doping level is necessary in InGaAsDnP Heterojunction Bipolar Transistors (HBTs) to achieve high device performances However, excessive diffusion of ptype dopants from the base to the emitter during growth or post-growth technological processes causes severe degradations of these performances. Consequently, the understanding and the control of Be diffusion in epitaxial layers are needed Investigations on Zn and Be diffusion mechanisms in the binary and ternary InP based compounds are still limited [ 1,2] The beryllium diffusion mechanisms have been considered by some authors to be similar in GaAs and InGaAs [2] The published results are contradictory and, to our knowledge, the point defect equilibrium has never been clearly discussed [2-71. Moreover, a complete study including model and satisfactory fitting of experimental Be diffusion profiles in InGaAs epitaxial layers for a large scale of experimental conditions is still lackingIn this work, using two approaches, the Boltzmann-Matano method and point defect nonequilibrium hypothesis, we show that a good agreement could be obtained between experimental and simulated Be diffusion profiles B-Theoretical study B. I -The Boltmunn-Mutuno methodUnder our experimental conditions, the Boltzmann-Matano transformation has to be modified in [8]:where xo is the location at which D is determined, C(0,t) is the surface concentration and (dC / dx),-, is the concentration gradient at x = xo Using the hypothesis of long diffusion time, doping layer could be considered as a thin layer Analytical solutions of the Fick's second law (error-function and Gaussian distribution) for different initial conditions (thick and thin films respectively) coincide for long diffusion times relatively to diffusion depth 0-7803-31 79-6196 $5.00 0 1 996 IEEE 189