Electroluminescence Studies Of Si Bulk Materials Using Al-Si Schottky Diodes
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Mat. Res. Soc. Symp. Proc. Vol. 486 ©1998 Materials Research Society
TA, and Si-2TO phonon assisted transitions were observed at 40 K, and the Si band-to-band recombination related emission can persist to room temperature. EXPERIMENTAL DETALS The Schottky diodes were made in the following way. 2000 A aluminum was deposited on the surface of n-type Si wafers with a resistivity value of -10 Q2-cm and
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patterned by photolithography for forming a series of 200 x 500 pm2 electrodes with a spacing of 150 pm, as shown in Fig. 1, with Fig. I Schematic cross section of Al-Si Schottky no passivation treatments. diodes fabricated for EL measurements The experiments were carried out on a pair of face-to-face Schottky diodes. In this case, the measured I-V characteristics of these pair of diodes are very symmetric and the total current passing through the devices is limited by the one of diodes that is in a reverse bias condition. The EL measurements were performed using a constant current mode. The carrier injection was done by applying a 0 - +V pulsed bias voltage on one diode while the adjacent one was grounded. The devices were mounted on a ceramic sample holder, and inserted into a cryostat, with a close contact to the copper cold finger, where we can measure and control temperatures through a built-in resistive heater. The electric pumping was realized by applying a series of square pulses (200 Hz) with 50 % duty cycle supplied by an HP 4150 pulse generator on the Schottky devices. The emitted light from the device was then collected by a lens and focused on the entrance slit (1 mm) of an Oriel 77276 single grating monochromator. After dispersion through the monochromator, the light was detected by a North-Coast liquid nitrogen cooled Ge detector (Model EO-817p, -10 gts response). Standard lock-in technique was used to record the measured EL intensity. For time-resolved EL measurements, DC output from another North-Coast Ge detector (Model EO-817s, -200 ns response) was recorded by a digitizing oscilloscope (Tektronix 620B). RESULTS AND DISCUSSION Fig. 2 shows EL spectra measured at various temperatures from such a Si Schottky diode pair at constant driving current of 10.5 mA. At - 40 K, an intense EL emission at 1.094 eV with a full width at half maximum value (FWHM) of 13 meV is observed, as has been interpreted as due to a TO phonon assisted process.' 0 At the same time, two weaker but clearly resolvable peaks at 1.132 and 1.032 eV, respectively, are also observed, which have been attributed to TAand 2TO-phonon assisted processes.' 0 The overall spectrum is very similar to the PL spectrum 158
observed at the same temperature. As the measurement temperature increases, the peak intensity of the Si-TO emission decreases while there is a peak width broadening. The main emission associated with the Si-TO transition persists at - 300 K with an FWHM value of 65 meV. The peak shape is asymmetric with an exponentially decaying tail towards the high phonon IFTJ-7 energy (1/e decay length is- 50 meV), which is
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