Layer intermixing in heavily carbon-doped AlGaAs/GaAs superlattices

Abstract

Interdiffusion of Al and Ga in heavily C-doped Al o . 3 Ga O . 7 As/GaAs supeduttice (SL) structures has been investigated quantitatively for a variety of ambient and surface encapsulation conditions. High-resolution photoluminescence (PL) at T = L 7 K was employed to evaluate the extent of layer intermixing after 24-h anneals at 825°C. From the shifts to higher energies of the PL peaks due to n = 1 e1ectron-to-heavy hole transitions in the quantum wells of the annealed SLs relative to the posi.tion of this peak in the as-grown crystal, approximate AI-Ga interdiffusion coefficients (D Al-Cia) have been determined for different annealing conditions. For all encapsulants studied the interdiffusion in C-doped crystals is accelerated with increasing AS 4 pressure in the annealing ampoule. This result disagrees with previously observed trends for Group II-doped p-type structures, which have led to the charged point-defect model (Fermi-level effect) of AI-Ga interdiffusion. The Si~\ N4 cap has provided the most effective surface sealing against ambient-stimulated layer interdiffusion, and yielded D A1 _ Ga ~ 1.5 -3.9X 10-19 cm 2 /s. The most extensive layer intermixing has occurred for uncapped SL annealed under As-rich ambient (D A1 -Ga ~3.3 X 10-]8 cm 2 /s). These values are up to -40 times greater than those previously reported for nominally un doped AlxGa1_xAs/GaAs SLs, i.mplying that the CAS doping slightly enhances host-atom selfdiffusion on the Group III sublattice, but significantly less than predicted by the Fermi-level effect. The discrepancies between the experimental observations and the model, are discussed. 5615 J.

Suppression of thermal atomic interdiffusion in InGaAs/AlGaAs QW laser structures

“…Since the carbon substitutes an As site on the group-V sublattice, the diffusion mechanism is different from the interstitial-substitutional model for Zn and Be diffusion, which substitute a group III atom in the lattice. The extent of intermixing for the case of carbon doping was reported slightly higher than in undoped samples, but much less than the prediction by a Fermi-level model 6 .…”

Layer Disordering and Carrier Concentration in Heavily Carbon-Doped AlGaAs/GaAs Superlattices

“…(1) CAI is the Al concentration in atomic fraction, ;L is half of the layer period and w is the half width of the initial Alo. 4 Gao. 6 As layer where the origin of the spatial coordinate x is placed at the center of the layer.…”

“…6 As/GaAs layers grown on semi-insulating GaAs substrate using the MOCVD method at -600 0 C. Each Al0. 4 Gao. 6 As layer is -30 nm thick and each GaAs layer -50 nm thick.…”

“…3 that the Ds value increases as the PAs 4 value is increased. This PAs 4 dependence of the Ds values suggests that CA, diffusion is governed by As self-interstitial ]"Ga-rich species, IAs, via the interstitial-substitutional mechanism (the kick-out mechanism [19]) according to the reaction <*-o As As' (4) In reaction (4) C and I 0 are respectively a singly-negatively-charged carbon interstitial atom I As and a neutral As self-interstitial atom. During CA diffusion, reaction (4) yields the local equilibrium condition…”

“…Using AlAs/GaAs SL, a few studies on the effect of carbon doping on Al-Ga interdiffusion have been conducted, but the results are not consistent [3][4][5]. The CA, diffusivity values have been measured [1,[5][6][7][8], and hole concentrations in carbon-doped GaAs and SL crystals have been reported to decrease when annealed at temperatures higher than -600°C [6,7,[9][10][11][12][13][14][15].…”