A model for the disordering of GaAs/AlAs-superlattices during zinc diffusion, which is consistent with recently established models for gallium self-diffusion and zinc diffusion in GaAs, is presented. Four coupled partial differential equations resulting from the model are solved numerically. In accordance with measured data in the literature, no disordering without zinc can result for temperatures around 600°C. Zinc diffusion, however, produces a large amount of gallium self-interstitials, which leads to a complete disordering of superlattices with a period thickness of 32 nm to a depth of about 0.8 μm within one hour. The used values for the diffusion coefficient and the equilibrium concentration of gallium self-interstitials are a consistent splitting of the gallium interstitial dominated self-diffusion coefficient.

We report on a study of disordering by the in-diffusion of a variety of Group IV and Group VI n-type impurities. Secondary ion mass spectroscopy, electrochemical C-V profiling, photoluminescence spectroscopy, and cathodoluminescence spectroscopy were used to determine the extent of interdiffusion, and the spatial distribution of impurities and native defects for impurity-induced disordering. In all cases, the n-type dopants enhance the Al-Ga interdiffusion coefficient over that due to an As overpressure of 2 atm alone. The Si-induced enhancement has been previously attributed to the change in Fermi level with doping and therefore should account for disordering using other n-type impurities. However, we observe important differences in the interdiffusion characteristics (diffusion rate, dopant profiles, energy and intensity of the deep-level emission) induced by Si or Ge, and that by S or Se. Whereas a strong correlation exists between the carrier concentration profile and the disordered regions in the Si-, Ge-, and Se-doped crystals, little direct correspondence is found for crystals doped with S. Instead, the disordering seems to be determined primarily by the presence of Group III vacancies, as is also the case in undoped crystals disordered by an As ambient alone. In addition, the deep level emission at 1.15 and 1.3 eV, which are associated with vacancy defects, correlates well with the extent of the Al-Ga interdiffusion.

Undoped 69GaAs/71GaAs isotope superlattice structures grown by MBE on n-type GaAs substrates, doped by Si to ∼3×1018 cm−3, have been used to study Ga self-diffusion in GaAs by disordering reactions. In the temperature range of 850–960°C, the SIMS measured Ga self-diffusivity values showed an activation enthalpy of 4 eV, and are larger than previously compiled Ga self-diffusivity and Al-Ga interdiffusivity values obtained under thermal equilibrium and intrinsic conditions, which are characterized by a 6 eV activation enthalpy. SIMS, CV, and TEM characterizations showed that the as-grown superlattice layers were intrinsic which became p-type with hole concentrations up to ∼2×1017 cm−3 after annealing, because the layers contain carbon. Dislocations of a density of ∼106-107 cm−2 were also present. However, the factor responsible for the presently observed larger Ga self-diffusivity values appears to be Si outdiffusion from the substrate, which was determined using CV measurements. Outdiffusion of Si decreases the n value in the substrate which causes the release of excess Ga vacancies into the superlattice layers where the supersaturated Ga vacancies enhance Ga self-diffusion.

The effect of the diffusion of monatomic hydrogen into InGaAs/AlGaAs quantum wells has been investigated using photoluminescence (PL) and Secondary Ion Mass Spectroscopy (SIMS). The structures were grown by molecular beam epitaxy and hydrogenated with a remote plasma. For In0.2Ga0.8AlxGA1-xAs quantum wells, hydrogenation significant increases the integrated PL intensity from bound excitons at 77 K. The enhancement of the PL is ascribed to removal of nonradiative recombination centers by hydrogen passivation of defects either at the heterojunction interface or within the epilayers. This PL enhancement (and defect passivation) increases as the Al concentration in the AlGaAs layers increases from 0 to 33 at%. A 50% increase of PL intensity is observed for InGaAs/GaAs. For 33 at%, the increase is a factor of 9. We also diffused deuterium into these InGaAs/AlGaAs quantum wells. The enhancement of the PL by deuteration was similar to that by hydrogenation. The isotopie substitution permits the determination of the depth distribution of deuterium in the multilayered structure by SIMS. SIMS results support the conclusion that more defects are passivated in the higher Al concentration samples.

We investigated the reason of the (imbalanced) accumulation of electrons in AIGaSb/lnAs/AIGaSb QW system in spite of the p-type conduction of undoped AIGaSb. It was found that the concentration of the accumulated electrons negligibly depended on the number of the interfaces, but increased linearly with the effective AlSb thickness. These results indicate that donor levels in AIGaSb are the dominant electron sources. We propose a model that the deep acceptors with larger concentration and donors coexist, and the electron accumulation depends on the energy position of the acceptor in AIGaSb with respect to the quantum level in the InAs well. Acceptor levels obtained experimentally are about 100 meV higher than the bottom of the InAs conduction band, and we succeeded in eliminating the electron accumulation by making the quantum level of the InAs well higher than this acceptor level. The origins of the donors and acceptors are also discussed.

We have performed Shubnikov-de Haas (SdH) measurements on the AlxGa1-xSb/InAs QW's with x from 0.1 to 1.0 under the negative persistent photoconductivity (NPPC) conditions and confirmed the prediction of Ionized Deep Donor model that the NPPC effect is a universal property for the materials containing ionized deep donors at low temperatures. The time-dependent recombination (electron capture) of the ionized deep donors is similar to that of DX centers. The saturated reduction of carrier concentration in the InAs well increases with increasing x, and rises steeply at about x=0.4. The concentration of deep donors which cause the NPPC in the AlxGa1-xSb/InAs QW's increases with the Al composition.

The effect of LT GaAs on the effective barrier height of the epitaxial Al/GaAs Schottky contact was investigated for the first time by inserting a thin LT GaAs layer (50 ∼ 500Å) between the in situ deposited Al film and conventional MBE GaAs epitaxial layer. The activation energy plot of saturation current for the devices showed that the effective barrier height exhibits a dependence on LT GaAs thickness and reaches a saturated barrier height when the LT GaAs layer exceeds a critical thickness. Compared to the samples which had no LT GaAs layer, the effective Schottky barrier height was decreased from 0.79 eV to 0.35 eV for the n-GaAs samples, and increased from 0.55 eV to 0.72 eV for the p-GaAs samples. The Schottky barrier height modification achieved by LT GaAs is tentatively explained in the terms of a bulk Fermi level pinning model. The work described here suggests that LT GaAs can be used as a defect source with controlled thickness to study defect associated phenomena such as Schottky barrier height modification.

Effects of rapid thermal annealing (RTA) with a SiNx encapsulant on molecular beam epitaxial GaAs are studied with deep level transient spectroscopy (DLTS) measurements and x-ray photoelectron spectroscopy (XPS) measurements. The RTA was performed at various temperatures form 800°C to 1100°C for 6sec. The electron trap EL2 is produced by the RTA above 850°C The EL2 depth profile produced after the RTA is fitted with a complementary error function. The SiNx cap layer is more effective to prevent the formation of the EL2 than the SiO* cap layer during the RTA, because the critical temperature of the SiNx cap where the EL2 concentration starts to increase is higher than that of the SiOx cap. Slight increase of the oxidized Ga atoms is observed after the RTA near the cap surface. The enhancement of the EL2 trap is discussed considering the outdiffusion of Ga atoms into the cap layer during the RTA.

In this paper we have studied the Einstein relation for the diffusivity-mobllity ratio (DMR) in small-gap superi at tices (SLS) with graded structures under magnetic quantization by formulating a new dispersion law. It is found, taking inAs/ GaSb SL as an example that the DMR increases in an oscillatory way with increasing carrier degeneracy due to SdH effect. The DMR in SL. is greater than that of the constituent materials. The theoretical results are in agreement with the suggested experimental method of determining the DMR in degenerate materials having arbitrary dispersion laws.

The unique properties of 3d-transition elements in silicon are reviewed that are essential for an understanding of gettering phenomena. Transition-element-gettering techniques are divided into two groups, depending on whether or not the dominant gettering mechanism operates during annealing or cooling down of silicon wafers. Experiments that identify the gettering mechanism are presented for oxygen precipitation-induced gettering (internal gettering) as well as phosphorus-diffusion gettering. It is concluded that only the latter technique operates during high-temperature treatment.

Generic and interaction aspects of oxygen precipitation, related defect formation and denudation in Cz-Si wafers are presented. Bulk defect profiles and homogenization control are shown to be achievable by proper design of post-growth annealing.

Gettering-related phenomena are discussed including stacking fault-rich bulk defect structures and peculiarities in different epitaxy systems.

Several aspects of metal gettering at internal oxide particle sites in Cz Si have been studied by ‘haze tests’, scanning infra-red microscopy (SIRM) and transmission electron microscopy (TEM). Haze tests indicated that complete gettering of Cu, Ni, Co and Pd can occur even when the amount of oxygen precipitated is below the detectable limit. TEM showed that the gettering of Cu, Pd and Ni proceeds by one of three different self-perpetuating mechanisms involving oxide particles and associated dislocations, the particular mechanism depending on the oxide particle size and the metal type. Haze tests and SIRM showed that for Cu and Ni there were minimum oxide particle number densities for effective gettering, and also maximum oxide particle number densities above which the additional oxide particles played no role in the gettering. These number densities depended on the metal type and specimen cooling rate. For all of these gettering behaviours, mechanisms are suggested to explain the results. The SIRM was also used to investigate for Cu and Ni the thermal stability of the gettering sites and the precipitated metals. The results showed that during repeated heat treatments the gettering occurs by a dynamic process.

Some gettering processes like internal gettering or backside damage gettering base on heterogeneous precipitation of metal impurities at defects in pre-de ter mined parts of silicon wafers during cooling from high temperatures. We consider microscopic properties of effective heterogeneous nucleation sites for cobalt, nickel and copper impurities from the fundamental point of view of suicide precipitate formation. We follow the basic concept that such gettering sites are defects which allow fast precipitation, i.e. which remove kinetic limitations known from homogeneous precipitation of these impurities at small supersaturation. For Co and Ni it follows that distorted lattice sites in the core of dislocations may establish high incorporation rates of interstitial atoms into suicide particles, whereas for Cu sinks for silicon self-interstitials are suitable gettering sites.

We present a new experimental approach to studying the mechanism of intrinsic gettering of Fe in Czochralski silicon crystals. We present our experimental method and results for as-grown and intrinsic gettered wafers with high and low-level Fe surface contamination. We found that when annealing at the Fe supersaturation temperature, Fe concentration decreases faster in intrinsic gettered wafers than in as-grown wafers. Concentration saturated with annealing time for each sample and the saturated Fe concentration followed a simple Arrhenius relationship. Re-emission of Fe from the bulk defect region occurred above the gettering temperature. We conclude that in intrinsic gettering, Fe precipitates preferentially in the bulk defect region when the Fe impurities supersaturate as temperature drops.

Rapid thermal annealing was shown by EBIC to increase the minority-carrier diffusion length in cast polycrystalline silicon. The beneficial effect is due to a deactivation of intragrain defects (mainly dislocations) and is stable against post-RTA annealing up to at least 600 °C/ 10 min.

Phosphorus gettering by diffusion from a POCl3 source was applied to matched wafers cut out of the same region of a cast ingot. Light Beam Induced Current mappings with wavelengths in the range between 840 and 980 nm lead to follow the variation of minority carrier diffusion length after gettering at 900°C for 120 and 240 mn, especially near extended crystallographic defects like dislocations and grain boundaries.

The mappings show that after the gettering treatments, the local values of L increase due to the reduction of the recombination strength of extended defects and to the improvement of the homogeneous regions of the grains.

As SIMS analyses indicate that Fe, Cu and Ni atoms are gettered, it is reasonable to assume that these impurities were initially dissolved in the grains and also segregated at the extended defects.

Present methods for minimizing stacking fault defects, generated during oxidation of silicon, include damaging the back of the wafer or depositing poly-silicon on the back. In either case a highly defective structure is created and mis is capable of gettering either self-interstitials or impurities which promote nucleation of stacking fault defects.

A novel method of minimizing these defects is to form a patch of porous silicon on the back of the wafer by electrochemical etching. Annealing under inert gas prior to oxidation may then result in the necessary gettering. Experiments were carried out in which wafers were subjected to this treatment. Subsequent to oxidation, the wafers were etched to remove oxide and reveal defects. The regions of the wafer adjacent to the porous silicon patch were defect-free, whereas remote regions had defects. Deep level transient spectroscopy has been used to examine the gettering capability of porous silicon, and the paper discusses the mechanism by which the porous silicon getters.

We have investigated the rapid thermal diffusion of phosphorus into p-type silicon from a spin-on coated film as a function of the process temperature and time duration. The electron diffusion length LD measurements performed by the Surface PhotoVoltage (SPV) method present evidence for a get-tering phenomena since the LD values of the diffused samples are significantly improved. This result is important for the future of RTP in the area of silicon devices where carrier transport is controlled by the bulk lifetime.

The effect of iron contamination in silicon on the properties of thermally grown thin oxides is studied through electrical modelling and experimental MOSDOT testing. Iron concentration is measured using a surface photovoltage / diffusion length technique. Failure mechanisms related to iron contamination are proposed. Contamination limits for various gate oxide thicknesses are defined. Experimental results show that reduction of oxide thickness from 20nm to lOnm requires a reduction in iron conntamination by 100 times.

We calculate the interaction (segregation) energies Egegr between the extended lattice defects (dislocations and grain boundaries) and impurity atoms in semiconductors by using a microscopic electronic theory. In particular, we use the tight-binding recursion method coupled to the generalized zeros-and poles method and investigate the interaction between the extended lattice defects and various kinds of the impurity atoms in semiconductors (Si). For the systematic understanding of the impurity gettering, we consider a wide variety of impurities, both sp-valence and transition metal impurities, Ti, V, Cr, Mn, Fe, Co, Ni and Cu. We will show that the variation of the gap states plays an important role in determining the interaction energy Esegr between the impurity atom and the extended lattice defects- We also discuss the passivation of the extended lattice defects by interstitial light impurities like hydrogen in Si crystal, we present a simple physical interpretation of the impurity gettering and passivation in semiconductors.