C. B. Norris

Introduction rates and annealing of defects in ion‐implanted SiO2 layers on Si

The introduction rates and isochronal annealing behavior of structural defects created by atomic collision or ionization in SiO2 layers thermally grown on Si in O2 and steam are investigated by measuring the induced volume compaction for ion and electron bombardments. The use of compaction measurements permits study of the introduction and annealing of defects with little confusion from changes in the charge state of the defects. The structural damage created by ion energy deposited into atomic collisions is found to be complex, possibly consistent with a thermal process involving reordering of the noncrystalline network of Si–O tetrahedra, and to anneal in a slow featureless manner beginning around 300°C and returning to the original density near the original growth temperature. The structural damage created by ion or electron energy deposited into ionization is identified with broken Si‐O bonds and found to anneal completely in a single well‐defined stage centered at 650°C. The ionization‐induced struct...

Ionization dilatation effects in fused silica from 2 to 18‐keV electron irradiation

We have used low‐energy electron irradiations in conjunction with a bending‐cantilever‐plate technique to investigate the volume dilatations produced by ionization effects in fused silica. Our irradiations generally cause compaction in agreement with previous data from high‐energy electron irradiations, but we consistently observe a slowly saturating compaction‐dose relationship rather than the sublinear power‐law relationship seen in the high‐energy data. Our results show agreement with the apparent ionization compaction effect extracted from low‐dose‐rate 1H+‐ion‐implantation experiments. We find no dose‐rate dependence in the electron ionization compaction effect, in marked contrast with the apparent ionization compaction effect in the implantation experiments. We therefore conclude that the enhancement of the apparent ionization compaction effect at high dose rates in the implantation experiments results from an interaction between the ionization and the atomic displacements accompanying the implanati...

Effects of Cd‐vapor and Te‐vapor heat treatments on the luminescence of solution‐grown CdTe:In

We have employed cathodoluminescence at 80–300 K in the first comprehensive study of the effects of Cd‐vapor or Te‐vapor heat treatments on the luminescence of solution‐grown CdTe:In. The broad 1.4‐eV band present in as‐grown material is weakened by Te firing and typically enhanced by Cd firing. These results do not support earlier connections between this luminescence and the VCd‐InCd complexes predicted by defect chemistry calculations to be dominant in CdTe:In. Alternatives to straightforward interpretation are discussed for both experiments and defect modeling. The effects of the heat treatments on the injection‐level dependence, frequency response, and temperature dependence of the 1.4‐eV luminescence are described. This luminescence arises from localized transitions within compact complexes in our as‐grown material, but different species of complexes or competing transition mechanisms are involved in heat‐treated material. The edge emission, present in both as‐grown and fired material, peaks near 1....

Depth‐resolved cathodoluminescence in undamaged and ion‐implanted GaAs, ZnS, and CdS

Here we report a variety of results obtained by using sequences of luminescence spectra excited by 1–20‐keV electron irradiation to carry out in situ studies of depth‐dependent optical activity in luminescent crystals. Data are shown for various samples subjected to localized damage from ion implantation: GaAs implanted with Cu+, ZnS implanted with Ar+ and Cu+, and CdS implanted with Ar+ and H+. Semiquantitative interpretation of the results shows that the depth‐resolved cathodoluminescence measurements can have unique value in characterizing the effects of ion‐implantation lattice damage. In this case cathodoluminescence can be excited from depths ranging from much shallower to much deeper than typical implant depths. In addition, the use of depth‐resolved measurements on nominally undamaged ZnS crystals reveals the presence of weak near‐surface luminescence bands despite careful surface preparation. This result makes it clear that luminescent center profiling by layer removal methods can lead to erroneo...

The origin of the 1.59‐eV luminescence in ZnTe and the nature of the postrange defects from ion implantation

We describe constituent‐vapor heat‐treatment experiments on ZnTe which indicate that the 1.59‐ eV luminescence in this material is VZn ‐related. The effects of Ga or I doping suggest further that the band is associated with some species of VZn ‐donor complex. This understanding of the 1.59‐ eV luminescence provides additional insight into our earlier study of postrange‐defect introduction in ion‐implanted ZnTe. The observed survival of the incumbent 1.59‐eV band in the postrange zone is discussed in relation to the conclusion from earlier published studies that Zni are the dominant postrange defects in ZnTe. We conclude that Zni are not strongly involved in the observed postrange damage. To the contrary, our work gives some indication that VZn ‐ and/or VTe ‐related centers are formed in the postrange zone.

Cathodoluminescence studies of anomalous ion implantation defect introduction in ZnTe

Shallow 100‐keV Xe+ ion implantations in CdTe are shown to introduce at least two species of 300 K‐stable defect complexes to depths of at least several thousand angstroms beyond the calculated projected ion range. The predominant defect species, which is nonradiative in the range 1–1.6 eV, produces severe quenching of the native 1.4‐eV cathodoluminescence excited from micron depths. Measurements of the injection level dependence of the quenched 1.4‐eV luminescence show that the quenching occurs primarily through the introduction of additional recombination centers rather than through the annihilation of native luminescence centers. Another defect species gives rise to an implantation‐induced band near 1.2 eV. The 1.2‐eV defects are more localized than the quenching defects and appear to be concentrated primarily at depths of several thousand angstroms beyond the projected ion range. Our experiments, which were performed on Te‐rich donor‐compensated CdTe, show that the anomalous defect introduction is sen...

Investigation of static electron irradiation effects in bulk Si and thin Si films at energies far below threshold

This paper investigates the defect production in Si reported to occur at electron irradiation energies far below the theoretically predicted 170‐keV bulk‐damage threshold. In contrast to published results, our experiments show no permanent resistance changes in bulk samples at fluences as high as 2×1018 20‐keV e/cm2 (78 K). Furthermore, fundamental damage studies using EPR techniques and optical spectroscopy confirm that fewer than 10−4−10−5 atomic displacements occur per 20‐keV electron. These results disagree with previous studies of irradiation‐induced resistance changes in bulk samples and epitaxial films from which it was indirectly determined that subthreshold atomic displacements appear following ionization of a Si K‐shell electron. However, we do find large resistance decreases in p‐type Si/spinel films at fluences ≳1015 20‐keV e/cm2 (300 K) that appear similar to anomalous results in the literature. But the energy and fluence dependences of the resistance change in our experiments are correctly p...

Cathodoluminescence studies of anomalous ion implantation defect introduction in lightly and heavily doped liquid phase epitaxial GaAs:Sn

The anomalous postrange defect introduction produced by shallow ion implantation in GaAs has been investigated in Sn‐doped liquid phase epitaxial (LPE) material using depth‐resolved cathodoluminescence in conjunction with layer removal by chemical etching. 100‐keV Ne+ or 200‐keV Zn+ ions were implanted into lightly or heavily Sn‐doped LPE layers at temperatures between 80 and 300 K. All implantations were subsequently annealed at 300 K. Although the projected ion ranges for the implants were on the order of 1000 A, significant postrange damage was observed at far greater depths. At depths up to several microns, the damage introduction produced severe nonradiative recombination but simultaneously caused an apparent increase in the concentration of incumbent luminescence centers responsible for an extrinsic band near 1.39 eV. A weak damage‐related band near 1.2 eV could also be seen in one instance. At depths of 5–30 μm, the postrange damage had the opposite effect of annihilating incumbent 1.39‐eV luminesc...

Further investigation of the 1.4‐eV luminescence in solution‐grown CdTe:In

Previous attempts to understand the mechanism responsible for the 1.4‐eV luminescence in solution‐grown CdTe:In were inconclusive because the measured combinations of injection level dependence, frequency response, and temperature dependence did not clearly indicate whether the transition originated from a band state or from a localized level associated with a compact complex. This paper reports the discovery of CdTe:In material in which temperature‐dependence data show that the 1.4‐eV luminescence transition cannot originate at a band edge. However, the spectrum, injection level dependence, and frequency response of the 1.4‐eV luminescence in the present material do not differ greatly from corresponding measurements on previous materials. The new data are presented in detail and include the first extensive measurements of the thermal broadening of the 1.4‐eV luminescence.

Cathodoluminescence studies of postrange defect introduction from ion implantation in CdSe

Cathodoluminescence measurements in conjunction with layer removal by chemical etching show that shallow 200‐keV Xe+ ion implantations cause significant postrange defect introduction in CdSe. Strong spectral changes are present at depths an order of magnitude beyond the calculated projected ion range (∼500 A). There is significant residual damage at depths greater than a micron in some instances. Implantation at 80 K yields deeper and more severe 300‐ K stable postrange defect introduction than does implantation at 300 K. One component of the postrange damage enhances nonradiative (<1 eV) recombination. The introduction of, or increased prominence in, deep‐center luminescence near 1.4 eV is tentatively associated with cadmium vacancy (VCd) introduction in the postrange zone. The simultaneous strong growth in the prominence of luminescence near 1.7 eV is explained by the novel interpretation that incumbent interstitial alkali impurities (Na, Li) are reacting with ion‐implantation‐induced VCd to enhance the...