Simulation of beryllium diffusion in the base layer of InGaAs/InP heterojunction bipolar transistors

Abstract

To explain the observed beryllium diffusion profiles in the InGaAs base layer of InGaAs/InP heterojunction bipolar transistors, the most basic form of Frank - Turnbull mechanism is proposed and implemented in a computer simulation program. A double profile is obtained which may be explained by the reduction in the vacancy concentration in the bulk of the crystal below its equilibrium concentration. Calculated profiles are computed and compared with our experimental profiles and with other beryllium diffusion profiles available in InGaAs. Some parameters such as diffusion time, diffusion coefficients, concentrations and vacancy bulk generation are investigated. The effect of V/III ratio on post-growth annealing profiles is also simulated. The point defect concentration in epitaxial layers during beryllium diffusion in InGaAs is discussed.

Study of beryllium diffusion mechanisms in InGaAs epitaxial layers grown by CBE

“…Investigations on p-type dopant diffusion in InP based epitaxial compounds, in particular Be in InGaAs, are still limited [1,2,12]. In a previous paper, we found that the diffusion coefficient is time independent under our experimental conditions.…”

“…Indeed, only a small but very rapidly diffusing fraction of (c) Be atoms is of interstitial type. Furthermore, there is no real experimental possibility of estimating the C eq i value which mainly depends on epitaxial method and growth parameters [2,12,20]. Consequently, in the initial doped layer, the Be interstitial concentration C eq i was chosen to be about two orders of magnitude lower than C eq s , and it was set at zero in the undoped layers.…”

“…Thus, we have deduced from the Boltzmann-Matano analysis that the Be effective diffusion coefficient is constant for high concentrations, and proportional to the square root of concentration for low concentrations [1]. Otherwise, considering point defect nonequilibrium conditions, a first simple model has already been proposed using uncharged species [12].…”

Simulation of p‐type diffusion in compound semiconductor: the case of beryllium implanted in InGaAs

“…However, some questions concerning peculiarities of beryllium diffusion are still unresolved because of the limited experimental data. For example, at an earlier stage of investigations it was believed that the diffusion occurred due to the Frank-Turnbull mechanism that involved a vacancy [6] or due to combination of kick-out and the Frank-Turnbull mechanisms [10]. At the present time a kick-out mechanism due to interaction of group III self-interstitial III I q+ with substitutionally dissolved impurity atom Be -via reaction…”

“…Therefore, many efforts were made to investigate experimentally Be diffusion in compound semiconductors [2][3][4][5][6][7][8][9][10][11][12][13][14]. Many efforts also were made to simulate Be diffusion [1,[6][7][8][9][10][11][12][13][14]. However, some questions concerning peculiarities of beryllium diffusion are still unresolved because of the limited experimental data.…”