Diffusion of Cd in GaAs and its correlation with self-diffusion on the Ga sublattice

Abstract

Cd diffusion into GaAs single crystals has been investigated in the temperature range 756–1201 °C. Penetration profiles measured by secondary ion mass spectroscopy and spreading-resistance profiling agree with each other and are numerically reproduced on the basis of the kick-out diffusion mechanism. A major involvement of vacancies via the dissociative mechanism can be excluded. This enables us to deduce from the Cd profiles effective Cd diffusivities (Dseff) as well as Ga diffusivities (DISD) mediated by doubly positively charged Ga self-interstitials (IGa2+). The Dseff values obtained from As-rich and As-poor ambients are mutually consistent. The same holds true for the DISD data. Reduced to 1 atm of As vapor pressure and electrically intrinsic conditions the Cd diffusion coefficient results as 1.76×104 exp(−4.80 eV/kB T) cm2 s−1 and the IGa2+-related self-diffusion coefficient as 3.5×104 exp(−5.74 eV/kB T) cm2 s−1. The present data provide strong evidence that in heavily p-doped GaAs atomic transport related to the Ga sublattice is governed by self-interstitials rather than vacancies.

Gallium interstitial contributions to diffusion in gallium arsenide

“…Earlier experiments that indicated that the more highly positively charged states (+2 and +3) of gallium interstitials are the most important charge states for diffusion, on the other hand, were prepared with more significant concentrations of p-type dopants. 2,6,7,67 Our calculations support this conclusion as well, because this material was prepared under the more heavily p-doped conditions which favor gallium interstitial diffusion in the +2 or +3 charge states. The authors of one of these papers noted that there were difficulties involved in using +2 charged gallium interstitials to properly fit the diffusion profiles in the regions with low concentrations of dopants, and that the solution to these difficulties would probably involve the use of +1 charged interstitials in the model, in addition to +2 and +3 charged interstitials.…”

“…The authors in Refs. 3 and 8 conclude from their own measurements and from re-analysis of the results of Bösker 6,7 that interstitial gallium in the neutral and singly positive charge states are partial contributors to gallium diffusion, with gallium vacancies contributing more strongly over much of the experimentally accessible range of stoichometry and doping level. Under arsenic-rich conditions, these authors observe an enhanced contribution of gallium vacancies to gallium diffusion.…”

“…2 Zucker et al studied the effects of ion-implanted zinc on the boundary profiles of superlattices of gallium arsenide and aluminum gallium arsenide and drew the conclusion that gallium interstitials were diffusing in a doubly or triply positive charge state. 5 Bösker et al diffused zinc into gallium arsenide under arsenic rich conditions 6 and cadmium into gallium arsenide under arsenic rich and arsenic poor conditions, 7 and also concluded that the doubly and triply positive charge states of gallium interstitials can adequately model the diffusion profiles. 6,7 However, in a later study employing isotope heterostructures with an implanted dopant to determine the relationship between zinc and gallium diffusion in gallium arsenide 8 it was proposed that it is the neutral charge state of the gallium interstitial and the neutral and singly-positive charge states of the gallium vacancy that are important in zinc-gallium codiffusion, contrasting with the earlier studies on interstitials.…”

“…5 Bösker et al diffused zinc into gallium arsenide under arsenic rich conditions 6 and cadmium into gallium arsenide under arsenic rich and arsenic poor conditions, 7 and also concluded that the doubly and triply positive charge states of gallium interstitials can adequately model the diffusion profiles. 6,7 However, in a later study employing isotope heterostructures with an implanted dopant to determine the relationship between zinc and gallium diffusion in gallium arsenide 8 it was proposed that it is the neutral charge state of the gallium interstitial and the neutral and singly-positive charge states of the gallium vacancy that are important in zinc-gallium codiffusion, contrasting with the earlier studies on interstitials. In subsequent work, Bracht et al 3 examined zinc and gallium co-diffusion into the surface of gallium arsenide, further refining their conclusion that the diffusion profiles can be fitted successfully by requiring that the gallium interstitials which contribute to diffusion are in a neutral or singly-positive charge state.…”

Spreading-resistance profiling of silicon and germanium at variable temperature

“…4 -6͒, Ge, 7 and to a lesser extent in GaAs. 8 Recently, efforts have been undertaken to arrive at a better qualification and standardization of SRP operations on Si. 9 Another development pursues higher depth resolutions to accurately analyze the ever decreasing dopant-structure sizes of electronic devices.…”