The infrared spectrum of indium in silicon revisited A. Tardella, B. Pajot To cite this version: A. Tardella, B. Pajot. The infrared spectrum of indium in silicon revisited. Journal de Physique, 1982, 43 (12), pp.1789-1795. 10.1051/jphys:0198200430120178900. jpa-00209562 HAL Id: jpa-00209562 https://hal.archives-ouvertes.fr/jpa-00209562 Submitted on 1 Jan 1982 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. J. Physique 43 (1982) 1789-1795 DTCEMBRE 1982, 1789 Classification Physics Abstracts 71.55 - 78.50 The infrared spectrum of indium in silicon revisited A. Tardella and B. Pajot Groupe de Physique des Solides de l’Ecole Normale Supérieure, Université Paris VII, Tour 23, 2, place Jussieu, 75251 Paris Cedex 05, France (Reçu le 27 mai 1982, révisé le 22 juillet, accepté le 23 août 1982) Résumé. 2014 Le spectre d’absorption de l’indium dans le silicium a été mesuré dans des conditions où l’élargisse- ment des raies par effet de concentration est négligeable. Avec une résolution appropriée, on détecte 17 transitions et les composantes d’un doublet serré sont attribuées à deux transitions calculées. A 6 K, la largeur intrinsèque des raies varie de 2,6 à 0,8 cm-1, ce qui indique un effet lié à la structure de la bande de valence du silicium. En utili- sant les résultats d’une mesure auto-cohérente de la concentration d’indium dans le silicium par une méthode spectroscopique, nous trouvons que l’élargissement par concentration est plus faible que ce qui avait été trouvé précédemment et que l’effet de paire semble inexistant dans les échantillons étudiés. Les mesures permettent aussi de détecter un élargissement thermique des raies entre 5 et 10 K. Abstract 2014 The absorption spectrum of In acceptor in silicon has been measured under negligible concentration broadening in order to obtain the true profile of the lines. With adequate spectral resolution, 17 transitions are detected and the components of a closely-spaced doublet are attributed to calculated transitions. At 6 K, the intrinsic width of the lines varies from 2.6 to 0.8 cm-1, indicating some resonance effect linked with the split-off valence band structure in silicon. Using the results of a self-consistent determination of the indium concentration in silicon by a spectroscopic technique, we find that in the samples studied the concentration broadening is smaller than that found previously and that no evidence for pairing is observable. These measurements also detect tem- perature broadening of the lines between 5 and 10 K. 1. Introduction. - Considering its excited states, indium-doped Si for samples ranging from a low substitutional indium in silicon is an effective mass- concentration limit to the highest concentration like acceptor despite its ionization energy of 157 meV, available by the growing technique used. With the which reflects a trend for group III acceptors, namely, samples with low In concentration, we detect more the heavier the element the higher the ionization excited levels - actually 17 - than previously report- energy. It has been used as a dopant for integrated ed [3, 4] and we measure accurately the intrinsic extrinsic Si detector arrays operating in the near IR width of the lines of the In spectrum. The integrated atmospheric window [1]. This has led to the availabi- intensity of the line at 1 176 cm-1 for the different lity of well-characterized crystals allowing meaning- samples investigated is used to obtain their In concen- ful linewidth studies and concentration broadening tration. The concentration broadenings observed measurements. Such studies have been previously are compared with those previously published [5] undertaken [2] and the fundamental work of Onton and phonon (temperature) broadening is detected et al. [3] on the absorption spectra of group III accep- in the low temperature range. tors in Si has provided a guide line for the subsequent experimental and theoretical work on these impurities, 2. Measurement techniques. - The float zone crys- but the role of temperature and of concentration tals used in this study were grown at the CENG and broadening for the lines other than those correspond- they were checked spectroscopically for residual B, ing to the first three IR-allowed excited states above P, Al, C and for 0, whose main vibrational line at the ground state have been overestimated, precluding, 1 136.4 cm-1 is contiguous to the In spectrum (see for instance, significant comparisons between the Table I). The exact indium concentration will be given highly excited states of the different acceptors. later, but in these samples In is the main electrically We present here some spectroscopical data on FZ active impurity over several orders of magnitude in Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:0198200430120178900 1790 Table I. - Characteristics of the Si (In) samples. The Hall mobility is measured at room temperature with a magne- tic field of 0.2 T. concentration. The samples, approximately con [8], suggest that a reflectivity value of 0.296 would 15 x 8 x d mm, d being a thickness appropriate to be more appropriate. the In concentration, were polished on the four large 3. results and discussion. - The In sides. They were fixed on their base by two dots of Experimental discrete observed between 1 145 and G.E. 7131 varnish on a sample holder in the compart- spectrum 1 255 to transitions the ment of a continuous flow cryostat (Oxford Instru- cm-’ corresponds from ground ments Model 204). The samples were cooled by the He state at Ev + 1 265 cm-1 (Ev + 156.9 meV) to excit- ed states the of = valence exchange gas and their temperature was assum- having symmetry the j 3/2 bands of silicon One can also observe ed to be that of a Ge thermometer mounted parallel (P3/2 spectrum). near 1 580 cm-1 the lines associated with excited to the sample at - 1 mm from it, on the sample holder. plj2 states the of the valence The temperature of the exchange gas could be varied having symmetry p 1 /2 band, by adjustment of the liquid He flow and of the current split from the P3/2 valence band by a spin-orbit sepa- ration of 42.62 meV at k = 0. The in a heater mounted on the heat exchanger. The sample (343 cm-1) p1/2 lines interfere with the continuum could be pumped laterally by band gap light by focuss- P3/2 acceptor and are broadened a Fano ing on it the output of a 70 W quartz halogen lamp they asymmetrically by effect The between the 1 state through a narrow band interference filter centred at [9]. separation T8+ ground 1.2 eV. The monochromatic beam transmitted by the and the j = 1/2 valence band is 1609.4 cm -1 The two most intense In 2 sample was detected by a mercury-cadmium telluride (199.6 meV). Pl/2 lines, p’ and 3 are located at 1 565 and 1 590 (MCT) detector with an AR coated Ge window. The p’ [3], cm-1, spectra, recorded digitally, were smoothed and lineariz- ed on line by a Hewlett Packard 9845 desktop compu- ter and then stored on a floppy disk. In order to obtain reliable figures for the background and for the inten- sities, plane parallel samples were used in most cases. The optical axis of the cryostat was tilted by - 50 with respect to the IR beam while keeping the sam- ple surface perpendicular to the beam. This avoids radiation reflected or transmitted by the sample being reflected back on it by the KRS5 cold windows distant by only 20 mm. Part of this reflected radiation, although defocussed, could reach the detector, lead- ing to an erroneous value of the absolute transmission of the sample. In some cases where interference fringes produced by the cold windows were observed in the spectra, they were eliminated by subsequent numerical filtering. The absorption coefficients of the In and 0 lines were measured either by taking the ratio of the transmission of a doped sample relative to that of an intrinsic sample or by measuring the absolute transmission of the doped sample and then removing the contribution We have assumed a phonon [6]. Fig. 1. - Recorder trace of the transmission spectrum of value of 0.300 for the silicon Measure- reflectivity. sample In-2, 4 mm thick. The two P1/2 lines observed are ments of the low-temperature refractive index of Si [7], at 1 565 and 1 590 cm-1. The two arrows indicate the reso- and the comparison between the calculated and experi- nance of the phonon replica of lines 1 and 2 of the P312 mental spacing of the excited states of donors in sili- spectrum with the P3/2 continuum. 1791 Fig. 2. - Ratioed spectrum of indium in sample In-1 Fig. 3. - Enlarged portion of the spectrum of figure 2. (Nln - 4 x 1015 at./cm3). The spectral band pass is 0.35 cm-1 The unresolved doublet 4AB is attributed to the 1 T$ - 1 r6 at 1250 cm-’. The losses of the detector response and and 1 r 8+ ...