W. G. Spitzer

Infrared reflectivity spectra and Raman spectra of Ga1−xAlxAs mixed crystals

Thick layers of Ga1−xAlxAs with uniform composition were grown by an isothermal liquid‐phase epitaxial technique. Infrared reflectivity and Raman‐scattering spectra were measured with the same samples. The clean ’’two mode’’ behavior was confirmed in the reststrahlen band region, and the infrared reflectivity spectra were analyzed by using a Kramers‐Kronig dispersion relation and by curve fitting to two forms for the classical dielectric function, one an additive form and the other a factorized form. The experimental data are in good agreement with the calculated TO and LO frequencies, when the Chang‐Mitra model has been modified with the assumption of a nonlinear dependence of the oscillator strengths on composition. In the Raman spectra, the disorder‐activated LA mode near 200 cm−1, a mode near 250 cm−1, and a background‐level change were observed and attributed to atomic disorder. In the infrared reflectivity measurements the major disorder‐induced effect was the increase in the TO and LO damping const...

Effects of thermal annealing on the refractive index of amorphous silicon produced by ion implantation

Precise infrared reflection measurements of the refractive index of silicon show that there are two well‐defined optical states of amorphous silicon produced by ion implantation. One is the as‐implanted amorphous state which is the high refractive index state produced by high fluence implantation of Si or P ions into Si samples. The other state, which has a refractive index intermediate between the as‐implanted and crystalline values, is induced by thermal annealing and is thermally stable until epitaxial recrystallization occurs.

Infrared Refractive Index and Absorption of InAs and CdTe

Transmission interference fringes from 2690 to 320 cm−1 for InAs and from 1330 to 320 cm−1 for CdTe have been analyzed with classical dispersion theory to obtain the room‐temperature dielectric constants. For InAs the dielectric constant between the band edge and the reststrahl e∞ and the static dielectric constant e0 are: e∞ = 11.8±0.1, e0 = 14.55±0.3; and for CdTe: e∞ = 7.05±0.05, e0 = 10.60±0.15. These values agree favorably with previously reported values. The absorption of InAs has been measured from 2500 cm−1, near the fundamental absorption edge, to 260 cm−1. Eight absorption peaks were observed between 444 and 269 cm−1 which are attributed to multiphonon combinations with the following characteristic phonon frequencies: TO1 = 222 cm−1, TO2 = 214 cm−1, LO = 196 cm−1, and LA = 143 cm−1. The transmission of CdTe has been observed from 10 000 to 220 cm−1. From 10 000 to 450 cm−1 the transmission is essentially constant at ∼60%. Below 400 cm−1 only two previously reported transmission minima were observed.

Si‐defect concentrations in heavily Si‐doped GaAs: Changes induced by annealing

Previously reported annealing effects on the carrier density and free‐carrier absorption are correlated with photoluminescence and localized vibrational mode infrared absorption measurements of annealed samples of heavily doped GaAs: Si. Annealing in the range 400≤TA≤750 °C produces the following qualitative changes: (i) a major reduction in the free‐carrier concentration ne, (ii) an increase in the carrier absorption cross section, (iii) a reduction of the SiGa localized mode absorption band, and (iv) the introduction of a new photoluminescence band at 0.98 eV. A defect model is proposed which is consistent with the observed changes. There is a major reduction in [SiGa], the Si donor concentration, which is a function of the anneal temperature between 400 and 750 °C. The reduction is probably through the formation of (SiGa − VGa) pairs. There is little change if any in [SiAs] the Si acceptor concentration. When TA = 400°C the ne = [SiGa] −[SiAs]. When TA = 600 and 750°C, a new acceptor is formed having c...

Local‐Mode Absorption and Defects in Compensated Silicon‐Doped Gallium Arsenide

Silicon is known to be an amphoteric impurity in GaAs. A large number of ir absorption bands have been previously reported for Si‐doped GaAs which has been compensated by Li or Cu diffusion. These bands, which are at frequencies above the pure GaAs single‐phonon spectrum, have been attributed to localized vibration modes of defects. The present experimental study extends previous work to show that all the observed bands (frequencies given in parentheses) are explicable in terms of the presence of the following defects: SiGa (384 cm−1), SiAs (399 cm−1) SiGa‐LiGa (374, 379, 405, 470, 480, 487 cm−1), SiGa‐CuGa (374, 376, 399 cm−1), and SiGa‐SiAs. (367, 393, 464 cm−1). These assignments appears to be consistent with results obtained by varying the Si concentration and by different thermal treatments.

High‐fluence implantations of silicon: Layer thickness and refractive indices

Refractive‐index measurements are given for amorphous Si produced by ion implantation. Reflection interference measurements in the frequency range 250≲ν≲ 7600 cm−1 were made for several Si samples implanted with P‐ion fluences between 1.0×1016 and 10×1016 ions/cm2 and ion energies between 0.20 and 2.7 MeV and for Si implants of 1.0×1016 and 3.0×1016 ions/cm2 and an ion energy of 0.30 MeV. The interference measurements were computer analyzed by using a model in which the damaged layer has a refractive index nD and extinction coefficient kD, and the substrate has a refractive index ns and ks=0. The optical constants of the two regions are smoothly connected by a transition region approximated by a half‐Gaussian curve of standard deviation σD. The finite‐width transition region is necessary for fitting the data. Excellent fits are obtained for literature values of ns and kD with the chi‐square being ?10−5. The value of kD has little effect on the analysis. Within the experimental accuracy a single curve for ...

Infrared reflection of ion‐implanted GaAs

Gallium arsenide has been implanted with nitrogen ions at 1–3 MeV and fluences between 3.3×1013 and 2.0×1017 ions/cm2. Room‐temperature infrared spectra are presented which show major changes in the reststrahl region. A sample having the highest fluence was isochronally annealed with 2‐h 100°C steps from 200 to 600°C, and the implantation‐induced reflectivity changes are annealed by 600°C. Changes of the dispersion parameters were determined by Kramers‐Kronig analysis as well as by curve fitting with classical dispersion (CD) analysis. Examples of dispersion parameters obtained by different analyses are compared and their validity is discussed. The data of nonimplanted and samples implanted with fluence up to 3.3×1014 ions/cm2 can be satisfactorily fitted with CD analysis assuming the material to be optically homogeneous. With this assumption, attempts to fit the data of samples with fluences ≥3.3 ×1015 ions/cm2 were unsuccessful. By extending the CD analysis to a layer model a reasonable fit was achieved...

Electrical and structural characterization of implantation doped silicon by infrared reflection

Abstract A physical model is presented for calculating infrared reflection interference spectra from ion implanted and annealed crystalline materials. The utility of the method is illustrated by presenting best fit spectra for a silicon sample implanted with 2.7 MeV phosphorous to a fluence of 1.74 × 1016 ions/cm2 and isothermally annealed at 500°C. Non-linear least-squares fitting of reflection data yields structural and electrical information about the implanted region with reasonable precision. The physical quantities determined are (i) the depth of the amorphous layer produced by implantation both before and during isothermal annealing, the thickness of the recrystallized material, and the widths of any transition regions, (ii) the dielectric properties of the amorphous and recrystallized material, and (iii) the characteristics of the free carrier plasma which yield the carrier density profile, the mobility near the carrier density maximum, and the carrier activation efficiency. Up to nine fitti...

Amorphous silicon produced by ion implantation: Effects of ion mass and thermal annealing

Characterization of the two optical states of amorphous Si produced by ion implantation is extended to include electron paramagnetic resonance, fundamental absorption edge, and density measurements in addition to infrared reflection. It is found that the properties of the two a‐Si states are not dependent upon the mass of the incident ion (12C, 29Si, 31P, 120Sn) or upon the anneal temperature for 400 °≤TA≤600 °C. The dangling‐bond density drops about a factor of 2 when the a‐Si makes a transition between the two states. The absorption coefficient also drops by more than a factor of 5, but the density of the a‐Si does not change when the transition occurs. The transition between states was not completed at TA=300 °C, so the annealing mechanism may be temperature dependent.

High‐resolution measurements of localized vibrational mode infrared absorption of Si‐doped GaAs

The infrared absorption due to excitation of localized vibrational modes (LVM) involving Si impurities in GaAs was measured at 80 K under high‐resolution conditions for 1×1018 cm−3≤[Si]≤5×1019 cm−3. Electrical compensation by Li diffusion or electron irradiation resulted in no observable differences in peak positions or linewidths for those LVM identified as SiGa, SiAs, and pair absorptions. These modes (including the individual lines composing the SiAs LVM) had intrinsic linewidths of 0.4 cm−1 which broadened as [Si] increased. In electron irradiated materials, an absorption band with major peaks at 366.63, 368.31, 369.53, and 370.7 cm−1 was seen to shift to lower energies by 9.9 cm−1 when 28Si was replaced with 30Si. Arguments are presented to suggest that the 366.63 cm−1 peak may be due to SiAs paired with a nearest‐neighbor native defect such as AsGa or a Ga vacancy. In Li compensated material, the isolated 7LiGa LVM was seen for the first time at 449.64 cm−1 as well as several additional unidentified...