W. Walukiewicz

Amphoteric native defects in semiconductors

We show that a new concept of amphoteric native defects with strongly Fermi level dependent defect formation energy provides the basis for a unified explanation of a large variety of phenomena in semiconductors. Formation of Schottky barriers, particle irradiation induced compensation, doping‐induced superlattice intermixing, and limits of free‐carrier concentration find for the first time a common simple explanation.

Coimplantation and electrical activity of C in GaAs: Stoichiometry and damage effects

We have coimplanted carbon and a series of elements (B, N, Al, P, Ar, Ga, As, and Kr) in GaAs to study the effect of both implant damage and stoichiometry on activation. Electrical activity of C was found to increase due to the additional damage caused by coimplantation of a heavy element regardless of the chemical nature of the coimplant. Maintaining stoichiometry by coimplanting a group III element further increased activation in substrates heavily damaged during implantation. Activation of 65±3%, corresponding to a sheet free‐carrier concentration of 3.5×1014 cm−2, was achieved by coimplanting Ga and annealing at 950u2009°C for 10 s.

Dislocation density reduction by isoelectronic impurities in semiconductors

A new mechanism for dislocation density reduction by isoelectronic doping is proposed. It is shown that the strain introduced by randomly distributed dopants lowers the vacancy supersaturation impeding dislocation formation via vacancy condensation. Trends in dislocation reduction through codoping with isoelectronic and electrically active impurities are discussed for the case of GaAs doped with indium.

Effects of rapid quenching on the impurity site location in Zn-diffused InP

The lattice locations of Zn atoms in heavily Zn‐doped InP single crystal have been investigated by ion channeling techniques. The InP samples were rapidly quenched in diffusion pump oil after high‐temperature Zn diffusion. Ion channeling experiments performed along various major crystal axes suggest that a large fraction (20%–30%) of the Zn atoms are in the tetrahedral interstitial position in the InP lattice. It has been found that although the maximum hole concentration is not significantly affected by the cooling rate, there is a substantial increase in the incorporation of Zn on substitutional and tetrahedral interstitial lattice locations in the rapidly cooled samples as compared to the slowly cooled samples. The consequences of these results for understanding the mechanisms leading to the saturation of the free‐hole concentration in compound semiconductors are discussed.

ORIGIN OF N-TYPE CONDUCTIVITY OF LOW-TEMPERATURE GROWN INP

It is shown with correlated magnetic resonance and electrical measurements that the PIn antisite is the prevailing defect in InP grown by molecular‐beam epitaxy at low temperature. The first ionization level of the PIn antisite is resonant with the conduction band, which makes the material n‐type conducting due to autoionization of the PIn antisite.

Direct evidence of carbon precipitates in GaAs and InP

Raman spectra of carbon‐doped GaAs and InP show two peaks which are characteristic of C clusters with sp2 bonding. The peaks are seen in C‐implanted GaAs and InP following either rapid thermal annealing or furnace annealing. The peaks are also seen in heavily doped epilayers following furnace annealing. Various mechanisms for C precipitation are discussed. Experimental evidence suggests that the loss of the group V component at the surface during annealing may play a role in the precipitation of C.

Substitutionality of Ge atoms in ion implanted AlSb

The substitution of Ge atoms into ion implanted AlSb is investigated by extended x‐ray absorption fine structure spectroscopy. Our results reveal that in the as‐implanted material, the implanted Ge atoms are equally distributed between two specific sites, one surrounded by Al atoms and the other surrounded by Sb atoms. After annealing at 750u2009°C for 5 s, the coordination number of the Ge atoms increases from ∼3 to ∼4 indicating solid phase regrowth of the implantation induced amorphous surface layer. Moreover, in the annealed AlSb, the substitution of Ge atoms into the Al sublattice dominates with an estimated GeAl]:[GeSb]∼0.8:0.2. These results suggest that Ge atoms act preferentially as donor species in AlSb.

Pressure dependence of the photoluminescence spectra of nitrogen‐doped ZnSe: Evidence of compensating deep donors

We have measured the photoluminescence spectra of nitrogen‐doped ZnSe under hydrostatic pressure. From the pressure dependence of the peak positions of the acceptor‐bound exciton and donor‐acceptor‐pair emissions, we show that highly doped samples have two donor‐acceptor‐pair transitions, one involving shallow and one involving deep donors. Our results confirm that one mechanism limiting the free hole concentration is compensation from this deep donor.

AMPHOTERIC SUBSTITUTIONALITY AND LATTICE DISTORTION OF GE IN INP

We have studied the electrical and structural properties of InP implanted with Ge ions (2×1015/cm2). The implantation was performed at both room temperature (RT) and liquid nitrogen temperature (LNT). After annealing at 850u2009°C for 5 s, both sets of samples exhibited n‐type conductivity. The n‐type activation efficiency in the RT implanted sample was about a factor of 2 higher than that in the LNT sample (15% and 8%, respectively). Extended x‐ray absorption fine structure spectroscopy (EXAFS) shows direct evidence of the amphoteric substitutionality of the Ge atoms in InP for both samples. The ratios of Ge on In sites to Ge on P sites, derived from the EXAFS results, are consistent with the electrical behavior of the samples. The EXAFS results also reveal that the Ge—In and Ge—P bond lengths in the RT sample are very similar to their theoretical values, but are very different from the original In—P bond length. A relaxation in the Ge—In bond is observed in the LNT sample, resulting in a Ge—In bond length v...

High dose Cl implantation in ZnSe: Impurity incorporation and radiation damage

The structural characteristics of ZnSe thin films grown by organometallic vapor phase epitaxy and implanted heavily with Cl ions (5×1015 and 1×1016/cm2) were investigated using ion beam techniques, x‐ray diffraction, and Raman spectroscopy. We have found that although the as‐implanted ZnSe layers were severely damaged, no amorphous layer was formed with an implant dose as high as 1×1016 Cl ions/cm2. Crystalline damage in the ZnSe layers was not fully removed even after annealing at 700u2009°C for 10 s. Ion channeling reveals that after annealing over 50% of the Cl atoms sit substitutionally in the lattice and they are preferentially located in the Se site. However, a significant fraction of the substitutional Cl are found to be slightly displaced from the normal Se sites. The projected displacement was found to be ≊0.2 A. Electrical measurements and Raman spectroscopy results suggest that a large concentration of Zn vacancies (VZn) are present in the annealed samples. We believe that the Cl displacement and t...