Be diffusion in molecular beam epitaxy-grown GaAs structures

Abstract

Beryllium diffusion is considered in heavily doped p-type GaAs structures grown by molecular beam epitaxy (MBE). Secondary ion mass spectrometry (SIMS) measurements performed on samples which underwent rapid thermal processing (RTP) experiments at 850 °C for 30 s show that (i) Be diffusion is faster in p/p+/p structures than in p/p+ ones and (ii) an increase of the As4/Ga flux ratio during the MBE growth affects Be diffusion only in p/p+ structures. These results are discussed by modeling Be diffusion according to a substitutional–interstitial diffusion mechanism where Be transition from substitutional to interstitial takes place by a kick-out process. The modeling procedure, which has been previously used to simulate Be and Zn diffusion in GaAs and in other related compounds, has been modified in order to account for the lacking of equilibrium in the initial concentration of Ga interstitials. It is shown that when the lacking of equilibrium is accounted for at the beginning of the annealing experiment, a satisfactory description of the SIMS results has been achieved in both p/p+ and p/p+/p structures, also considering samples grown by different As4/Ga flux ratios. The modeling results allow us to conclude that in the p/p+/p structures the concentration of point defects (e.g., IGa) in the regions cladding the base layer affects, to a major extent, Be diffusion during RTP, so that an efficient reduction of Be diffusivity is expected only when the whole structure is grown by high V/III flux ratios.