P. Mei

Comparative studies of ion‐induced mixing of GaAs‐AlAs superlattices

The species dependence of ion‐induced superlattice mixing has been examined in AlAs‐GaAs superlattice samples grown by molecular beam epitaxy. The interdiffusion of the superlattices induced by ion implantation with comparable ranges, doses, and subsequent thermal anneals were measured with secondary ion mass spectrometry. The effects of elements of comparable mass (Ga, As, and Ge) and comparable valence (Si and Ge) were studied. The experimental results show that Ga and As implantation cause primarily collision‐induced mixing, while Ge implantation results in collision‐induced mixing with additional impurity‐induced mixing beyond the implant range. In comparison with Ge, Si‐induced mixing is similar in nature though there is significant difference in the depth and extent of the mixing. The extent of mixing is found to depend on the local Ge or Si concentration.

Study of interdiffusion in a Te‐doped AlAs‐GaAs superlattice

The enhanced layer interdiffusion in Te‐doped AlAs/GaAs superlattices has been studied by secondary ion mass spectrometry. The superlattice sample was grown by organometallic chemical vapor deposition with Te doping at concentrations of 2×1017–3×1018 cm−3 during the growth process. In the temperature range from 800 to 1000 °C, the Al diffusion coefficient has an activation energy of 3.0 eV and is approximately proportional to the Te concentration. These results contrast sharply with Si‐induced mixing which, in an analogous experiment, yielded an activation energy of 4.1 eV for the Al diffusion coefficient with a high power law dependence on the Si concentration.

Conversion of InP/In0.53Ga0.47As superlattices to Zn3P2/In1−xGaxAs and Zn3P2/Zn3As2 superlattices by Zn diffusion

A standard 600 °C closed‐tube Zn diffusion into an unstrained InP/In0.53Ga0.47As superlattice was found to produce new superlattices containing Zn3P2 layers, and in some cases Zn3As2 layers. Crystalline properties and diffusion profiles were examined by transmission electron microscopy and secondary‐ion mass spectrometry. Initial doping of Zn enhances the diffusion of In and Ga and results in a superlattice of uniform In and Ga distribution. Upon further infusion of Zn, Zn3P2 forms selectively in the phosphorus layers and propagates from the surface while maintaining an atomically abrupt Zn3P2/In1−xGaxP interface. Zn3As2 conversion is also observed to occur under sufficiently stringent conditions. Diffusion of P and As was not observed.

DEPTH-DEPENDENT MIXING OF AN AlAs-GaAs SUPERLATTICE BY ION IMPLANTATION

The effects of implantation and annealing on an AlAs-GaAs superlattice grown by OMCVD is examined with SIMS (secondary ion mass spectrometry). Several 180 keV 28 Si + implants, with doses ranging from 3 × 10 13 to 3 × 10 15 cm −2 , are examined before and after a three hour 850 C anneal. While the implantation by itself causes some intermixing in the vicinity of the projected range, the 850 C thermal anneal induces significant mixing at depths well beyond the implant range. In the region of maximum implant damage, however, the post-thermal mixing effect is inhibited. Depth dependent diffusion lengths of Al and Si are derived from the SIMS data. The diffusion coefficient of Si is markedly enhanced in the mixed regions.

Mixing inhibition and crystalline defects in heavily Si‐doped AlAs/GaAs superlattices

Superlattice mixing in heavily silicon‐doped AlAs/GaAs superlattices has been examined by secondary‐ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM). Samples were grown by molecular beam epitaxy with Si concentrations of 1018 to 1020 cm−3 introduced during the growth process. Interdiffusion of Al was inhibited at a Si concentration of 1020 cm−3. Defect clusters and prismatic dislocation loops were found to be associated with Si concentrations of 1020 and 1019 cm−3, respectively. Si was observed by SIMS to segregate preferentially into the GaAs layers and TEM observation revealed defect formation in these same layers during the diffusion process, suggesting a strong correlation between Si segregation and defect formation. In the range of Si concentrations employed, the Al diffusion coefficient is found to vary as the third power of the estimated electron concentration, consistent with our previous results at lower concentrations. These results suggest that the diffusion inhibition at...

Silicon Induced Mixing of AlGaAs Superlattices – Behavior and Mechanisms

Mixing (or interdiffusion) of AlGaAs superlattice layers is greatly accelerated in the presence of Si doping. We have employed secondary ion mass spectrometry (SIMS) to monitor the depth dependence of the Al diffusion coefficient as well as the Si diffusion profile. Our results reveal unusually complex dependences on implantation and annealing conditions. To isolate the effects of chemistry and lattice damage, several structures were grown by molecular beam epitaxy (MBE) containing plateaus of Si concentration. The doping dependence and activation energy of Al diffusion were then evaluated in as-grown samples and in samples damaged by MeV Ga ion bombardment. To further elucidate the process, samples containing single or multiple implants of various dopants and impurities were examined. Microscopic and electrical characterizations were also performed. Al diffusion was found to be strongly inhibited by lattice damage and by very high Si doping levels. The Al diffusion coefficient has a high power law dependence on Si concentration while its activation energy is relatively unaffected by doping or lattice damage. A wide range of experimental and theoretical mixing studies are surveyed. Mixing models invoking Si pairs, divacancies, Fermi level arguments, and other mechanisms are critically assessed.

Study of the Carrier Concentration Effect on Si Enhanced AlGaAs/GaAs Superlattice Mixing

We have investigated the carrier concentration effect on AlGaAs/GaAs superlattice mixing enhanced by Si doping. The Al 0.01 Ga 0.99 As/GaAs superlattice sample with various Si-doping concentrations was grown by molecular beam epitaxy (MBE). Secondary ion mass spectrometry (SIMS) and carrier concentration profiling were used to characterize the Al diffusion and the free-carrier concentration profiles. The Al diffusion coefficients at 800 C show a high power dependence on the free carrier concentration which is not consistent with a Ga vacancy diffusion mechanism. A possible explanation can be provided by a mechanism based on a Si pair diffusion model.

Studies Of Ion Beam Enhanced Mixing Of AlGaAs Superlattices

The species dependence of ion induced superlattice mixing has been examined in AlAs-GaAs superlattice samples grown by molecular beam epitaxy. The interdiffusion of the superlattices induced by ion implantation with comparable ranges, doses and subsequent thermal anneals were measured with secondary ion mass spectrometry. The effects of elements of comparable mass (Ga, As, and Ge) and comparable valence (Si and Ge, Be and Zn) were compared. The experimental results show that Ga and As implantation cause only collision-induced mixing, while Ge implantation results in collision-induced mixing with additional impurity-induced mixing beyond the implant range. In comparison with Ge, Si induced mixing is similar in nature though there is a significant difference in the depth and extent of the mixing. The extent of the mixing is found to depend on the local Ge or Si concentration. The mixing effect of Be and Zn is predominately an impurity effect.