Vol.47,No.11,1996 Influence of Electrochemical Etching Current Density on Porous Si Luminescence Properties and Microstructure Kazuhiro SHIGYO *, Masahiro SEO *, Kazuhlsa AZUMI * and Hideaki TAKAHASHI * A porous silicon layer (PSL) was prepared on single-crystal p-type Si (100) wafers with electrochemical etching in HF solutions at different current densities to explore the effect of current density on the PSL luminescence properties and microstructure. Luminesence was evaluated by measuring photoluminescence (PL) spectra. The microstructure was observed FE-SEM, TEM, and CLSM. The surface composition was determined using using FT-IR The PL intensity emitted the PSL increased with increasing electrochemical etching current analysis. by density. TEM images indicated the PSL prepared on a specimen with specific 1kƒ m that Si a resistivity of consisted of dispersed ultrafine particles with a diameter of 2 `5nm. The structure the PSL prepared Si of on a Si specimen with specific resistivity 0.1ƒ m was and The microstructure (0.1ƒ m ) a of coarse columnar. PSL became fine granular with increasing current density. spectra that the surface concentration and FT-IR showed SiHx of decreased with increasing current density. From these results, concluded that the quantum PSL we confinement is operative on the visible luminescence from the and the surface compound consisting effect PSL, of SiHx surface states reducing the luminescence intensity. The electronic band models of the SiHx/PSL/ forms p- Si substrate are proposed to explain the visible PL mechanism. Key Words : Porous Silicon, Electrochemical Etching, Current Density, Microstructure, Luminescence Property Graduate School of Eng., Hokkaido Univ. (Kita-l3Jo Nishi-8 chome, Kita-ku, Sapporo-shi, Hokkaido 060)
Fig. la PL spectra of PSL prepared on Si specimen (p = 1 k Q m) with electrochemical etching in HF solution (26wt %) under galvanostatic conditions of different current density. Fig. lb PL spectra of PSL prepared on Si specimen (p = 0.1 Q m) with electrochemical etching in HF solution (17.6wt%) under galvanostatic conditions of different current density.
V ol.47,na11,1996 A B B C C Fig. 4 TEM images of PSL prepared with different electrochemical etching conditions as follows. Fig. 2 SEM images of PSL prepared on Si specimen (p= 1 kqm) with electrochemical etching in HF solution (26wt%) under galvanostatic conditions of different current density. A B Fig. 3 SEM images of PSL prepared on Si specimen (p= 1 kqm) with electrochemical etching in HF solution (26wt%) under galvanostatic conditions of different current density.
Fig. 5A Anodic polarization curves of p-si (p = 1 k 52 m) in HF solutions of different concentration. (Potential sweep rate is 100mV Fig. 5C Schematic polarization curve of p-si for distinguishing between PSL formation and electropolishing surface. Fig. 5B Anodic polarization curves of p-si (p =0.1 52 m ) in HF solutions of different concentration. (Potential sweep rate is 100mV s-'. )
V ol.47,na11,1996 Fig. 6A FT-IR spectra of PSL prepared on Si specimen (p = lk Q m) with electrochemical etching in HF solution (26wt %) under galvanostatic conditions of different current density. Fig. 6B Logarithm of PL peak intensity as a function of relative surface concentration of SiHx. Standard PSL was prepared on Si specimen (p = lk Q m) with electrochemical etching (0.25kA m- 2, 600s) in 26wt% HF solution.
Fig. 8 PL spectra of PSL prepared on Si specimen (p - 1 kqm) with electrochemical etching (0.25kA m 2) in 17.6wt % HF solution for which the electric charge was varied. Fig. 7 CLSM reflectance images of PSL prepared on Si specimen (p = 1 k Qm) with electrochemical etching (0.25kA m '. 600s) in 26wt% HF solution. Fig. 9 Maximum PL intensity as a function of PSL thickness. PSL was prepared on Si specimen (p = 1 kqm) with electrochemical etching (0.25kA m-') in 17.6 wt% HF solution for which the electric charge was varied.
Vol.47,No.11,1996 A B Fig. 10 Electronic band model of the SiHx/PSL/p-Si substrate proposed for explanation of visible PL mechanism. A : Surface concentration of SiHX is high. B : Surface concentration of SiHx is low.
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