Photoacoustic spectrum of porous silicon irradiated by light
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Photoacoustic spectrum of porous silicon irradiated by light Toshio Kawahara, Takaharu Kiyotoo, and Jun Morimoto Department of Materials Science and Engineering, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka 239-8686, Japan
Ritsuyasu Koga, Sinsui Iwane, and Kenichi Tahira Department of Electronic Engineering, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka 239-8686, Japan
Toru Miyakawa Department of Computer Science, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino 275-0016, Japan (Received 4 March 1999; accepted 22 July 1999)
The photoacoustic (PA) spectra for the porous silicon samples irradiated during or after anodization are reported. The difference between the spectra for the irradiation conditions is discussed. The light irradiation time dependence of the PA spectra is shown. The irradiation after anodization causes the samples to luminesce in the blue region and enhances the photoluminescence signal intensity around 600 nm. It also reduces the PA signal intensity in the shorter wavelength region. The irradiation during the anodization causes enhancement only in the red-region luminescence.
I. INTRODUCTION
Porous Si (PS) shows an efficient visible roomtemperature light emission under both photoluminescence (PL)1,2 and electroluminescence (EL).3 PS can be generated from a single crystalline Si wafer by electrochemical anodization. So many research works have been undertaken to realize all the Si optoelectronic devices which are usually made from the compound semiconductors. Red light emission was first discovered from the highly porous structure.1 The tuning of emission wavelength was also reported. The blue shift of luminescence was achieved by the direct oxidation of PS by thermal treatment4,5 or the boiling process.6 Another method for tuning is photoinduced oxidation7,8 during or after anodization. On the other hand, the continuously tunable PL from red to blue was reported9 using light irradiation by a tungsten lamp, where only postanodization irradiation was carried out without any oxidation processes. The luminescence properties were mainly studied for PS including the surface-oxidized samples and the light-irradiated one. So far only photoacoustic (PA) experiments were completed on PS samples that did not have the blue shift or the processing light irradiation.10 We also have studied PS without the processing light irradiation using photoacoustic spectroscopy (PAS).11 PAS can detect the nonradiative recombination process contrary to PL which can detect radiative luminescence. The PA measurement sensitively detects the heat generated by the incident light beam as acoustic or elastic waves.12,13 PAS is rather J. Mater. Res., Vol. 14, No. 11, Nov 1999
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insensitive to the effects of scattering expected in porous structure and a suitable tool to study the luminescence of PS through the nonradiative processes. In this report, we describe the results of our PA measurement on t
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