O. J. Marsh

Electrical Behavior of Group III and V Implanted Dopants in Silicon

The anneal behavior of layers implanted with dopants from column III (B, Al, Ga, and Tl) and column V (As, Sb, and Bi) in silicon substrates has been investigated. The ranges of implant conditions were energy 20–50 keV, dose 1013–1015/cm2, and substrate temperature 23°–500°C. Hall‐effect and sheet resistivity measurements were used to determine the effective number of carriers/cm2 (Ns)eff and the effective mobility μeff. Analysis of nonuniform distributions of carrier densities and mobilities on these measurements shows that the values of (Ns)eff and μeff can be misleading unless the effect of the depth distributions is allowed for. These distributions have been determined in some cases by the use of layer removal techniques combined with Hall‐effect and sheet resistivity measurements. We find in well‐annealed implanted samples that the dependence of the mobility on carrier density follows that determined for bulk silicon. In many cases deviation from this relation can be accounted for on the basis of com...

Ion‐induced migration of Cu into Si

Ion bombardment of Cu‐contaminated Si surfaces with either 20‐keV Ne+ or 800‐eV Ar+ ions leads to enhanced migration of Cu into the bulk of the Si to depths comparable to the projected range of the incident ions. The migration proceeds sufficiently rapidly to prevent sputter removal of submonolayer amounts of Cu even though as much as 100 A of the substrate is sputtered away. The enhanced migration is probably caused by defect production during the slowing down of the incident ions. The depth distribution of the Cu following Ne+ or Ar+ bombardments was determined from backscattered energy spectra of 280‐keV α particles.

Impurity‐peak formation during proton‐enhanced diffusion of phosphorus and boron in silicon

The formation of a phosphorus or boron impurity peak in silicon has been observed following irradiation with monoenergetic protons. In this study we used a sample temperature of 700 °C, proton‐beam energies of 50–140 keV, proton‐beam current densities of ∼1 μA/cm2, and proton‐bombardment times of 3 min to 3 h. The resultant impurity profiles were obtained using Schottky‐barrier differential C‐V techniques.

High-fluence implantations of Ge into 〈111〉 Si

Abstract The annealing of radiation damage produced by room-temperature and 300°C implantations of 60 keV 72 Ge to fluences greater than 10 16 /cm 2 into 〈111〉 Si was investigated by backscattering and channeling analyses of 280 keV alpha particles. Implantation at room-temperature produced an amorphous layer which only partially reordered after anneal at 850°C. However, implantation at 300°C did not produce an amorphous layer, and after annealing at 1000°C, resulted in an essentially perfect crystalline alloy of SiGe having a uniform Ge concentration of 6 at.% over a depth of 1000 A. These results are also consistent with optical reflectivity data obtained on the sample surfaces in the 3–5.5 eV spectrum.

Backscattering Analysis and Electrical Behavior of SiC Implanted with 40 keV Indium

Based on backscattering analysis of SiC implanted with 40 keV In+, we have shown that an amorphous layer is formed at 23°C after a dose of 1 • 1014 In+/cm2. After 1200°C anneal the amorphous layer is largely recrystallized, and ~60% of the In atoms are along the [001] atomic rows of α-SiC. Although the measured projected range of the In+ agrees with that calculated by Johnson and Gibbons, the standard deviation in range is over three times greater than the calculated value. Little residual disorder remains after a 450°C implant of 3 • 1014, 40 keV In+/cm2 into β-SiC, and ~90% of the In atoms are substitutional following a 1200°C anneal. Although the disorder profile produced by the 23°C implant is comparable to the In distribution, the disorder profile obtained after the 450°C implant indicates a small disorder peak at depths near the maximum penetration of the In. No p-type conduction of the layers implanted at 23°C was observed after anneals up to 1700°C. However, a sample implanted with In+ at 350°C did show weak p-type behavior after implantation and after anneals of 1000°C or less. Following anneals of 1200°C no p-type conduction was observed, but rather i-layers of thickness comparable to that of the In+ penetration were formed in all the implanted samples. The lack of p-type conduction is attributed to donor type defects which persist to 1800°C. The i-layer thickness changed with anneal temperature, suggesting the presence of mobile defects which anneal at 1600°C.

Neutron Transmutation Doping of p-Type Czochralski-Grown Gallium Arsenide

We have studied the neutron transmutation doping process in bulk GaAs grown by the liquid encapsulated Czochralski technique. By choosing undoped, but initially p-type samples for irradiation, we observed the effects of transmutation doping with Se and Ge donors both at low doping levels as added compensation in p-type samples, and at higher doping levels as added donors in n-type samples. We found that a measurable fraction of NTD-produced Ge atoms act as acceptors rather than donors in our material.

Extrinsic Silicon Focal Plane Arrays - Influence Of Material Properties

For extrinsic silicon detector arrays, performance is optimized by a careful compromise among several material characteristics affected by growth and processing parameters. In this paper we discuss the role of the major and minor dopant concentrations on spectral response, spatial uniformity of responsivity, impact ionization and impurity band conduction. The impact of these on detector operational constraints is a key element in focal plane detector array design.

Measurements of 3 1P Concentrations Produced by Neutron Transmutation Doping of Silicon

The absolute concentrations of 3 1P, produced by the irradiations of float zone silicon samples in the Texas A§M University Research Reactor, have been measured to an accuracy of ± 10%. The neutron fluence was varied from 1016 to 1018n/cm2, which corresponded to 3 1P concentrations in the 1012 to 1014 atoms/cm3 range. The results are based on measurements of the absolute activities of 3 1Si by detection of 1.266 MeV gamma rays. Secondary standards of Fe were required for the larger neutron fluences. The 3 lp concentrations were compared to the concentrations of electrically active P following 850°C anneals for 1 hour. These concentrations were determined in the same samples from temperature-dependent Hall effect measurements at Hughes Research Laboratories. The two results agree to within experimental error, thus confirming that transmuted P in the 1012 to 1014 atoms/cm3 range is completely electrically active following 850°C, 1 hour anneals of float zone silicon. In addition, a corrected value for the gamma abundance of31Si was established to be 5.6 x 10-4 ± 10%.

Defects in Neutron-Irradiated Extrinsic P-Type Silicon

At the 1978 International Conference on Transmutation Doping in Semiconductors, we reported the initial results of a study of radiation defects in neutron-irradiated, low-oxygen extrinsic p-type silicon.1,2 In that initial study we observed two new shallow acceptor levels denoted A1 and A2 located near the valence band edge in the forbidden gap of Si. The activation energies for A1 and A2 were determined from measurements of Hall effect vs. temperature to be ∿0.03 eV and ∿0.04 eV, respectively, in irradiated Si:Ga. These defect centers were observable after annealing at temperatures between ∿575°C (below which temperature the centers were overcompensated by excess damage-produced donors) and ∿625°C. Damage-produced donors became observable at an anneal temperature of ∿500°C with concentrations well in excess of the total concentration of initial donors (measured) plus transmutation-produced phosphorus. These donors annealed away with increasing anneal temperature, and the concentration became too small to observe at an anneal temperature of ∿700°C. Annealing at 700°C to 850°C removed all observable radiation effects — both shallow acceptors and radiation-produced compensating donors. We also observed the shallow acceptors in low-temperature photoconductive spectral response measurements in our initial work, but no extensive study of the optical prperties of these centers was carried out.

Shallow Defect Levels in Neutron Irradiated Extrinsic P-Type Silicon

Two shallow levels, at 0.027 eV and 0.039 eV from the valence band, measured by Hall effect vs. temperature, have been observed in neutron irradiated, float zone (FZ) grown Si: Ga. The neutron irradiation was for the purpose of counter-doping residual boron by producing phosphorus by neutron transmutation 3 0Si (n, γ)3 1Si → 3 1P + β- to allow the Si: Ga to be used as extrinsic Si detector material. These defect levels are observable after 575° to 625°C anneals. Annealing at 700°C - 850°C removes observable radiation defects. Analysis of the Hall effect vs. temperature data indicates that the two levels are acceptors with concentrations in the range 1014- 1015/cm3, in excess of the B concentration of ≴ 2 x 1013/cm3 measured before irradiation. A proportionality between defect concentration and Ga concentration is observed. The shallow levels appear also in photoconductivity spectral response measurements at 5K. Observations of shallow levels in FZ-grown Si: Al and Si: In will also be discussed.