Laser-Stimulated Changing of Micromechanical Properties in the Monocrystalline and Porous Silicon
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(with linear size of 10 - 20 micrometer and even more) regular geometrical shape. It is possible to control sizes and density of such defects by giving the certain oxidation and cooling regimes of crystals thermotreatment (Fig. 1-3). Such oxidation defects with much smaller sizes are often considered as dislocation sources in literature. The peculiarity of obtained dislocation sources was that their plastic potential was frozen until the external actions was not applied to crystal. Under uniaxial tension of thin silicon monocrystals the start stresses of dislocation sources generation in preliminary oxidized samples were 5 ...7 and more times lower than in initial ones (Fig.4). At lower temperatures the start stresses of dislocation sources generation became equal, but dislocation ensembles pathes from sources were 6 ...10 times more than these in initial crystals (Fig.5). Initiatiating of dislocation generation by OD may be achieved by irradiation of Si crystal surface by pulsed laser radiation with 1,06 micrometer wave length. The threshold energy which2 is nessesary for dislocation generation by OD (at pulse duration of 4 ms) varies from 1* 105 j/m to 5 ° 105 j/m 2 at sample temperature range 293 ...573 K (Fig.6). This energy decreases with temperature increasing (Fig. 7). Unlike the thermal annealing the dislocation ensembles pathes from sources is almost independent from internal stresses values, but is defined by falling pulses energy and the number of pulses. Long term irradiation of Si surface by pulsed laser with energy pulses about threshold energy is the most effective. It is possible to control both the dislocation ensembles pathes and 2
'E 4
36-2
1100 1300 T, C Fig. 1. Variation of oxidation defects density with oxidation temperature. The oxidation time are 1 - 2 hours, 2 - 3 hours. 50 0 900
1000
2
40 &*30 S20
700
900
1100
1300
Fig.2. Variation of the oxidation defects size with oxidation temperature on the air. n - Si. 1 - 0,5 0m sm; 2. - 2,0 0m sm ta = 2 hours.
710
the dislocation density in the local areas of crystal surface by the accumulation of irradiation dose. The paper presents an extended study of monocrystal silicon samples surface layer affer their irradiation treatment as well as their treatment by specially chosen selective etchers, which allow to detect the dislocations on the crystal surface. It was noted that after the etch a rather thin layer of porous silicon was formed with the structure similar to amorphous state. Thus a simple effect of selective etchers on silicon surface allows to create a porous silicon near surface layer. It was stated that in flowing the current through a porous structure the electroluminescence effect in the visible area of irradiation was observed (Fig. 8). 30 -2 20 400
T,°*C800
1200
Fig.3. Variation of oxidation defects size with quenching temperature of the silicon crystals oxidized at T = 1150 0C (1) and at T = 1180 0C (2) during 2 hours.
160
3~ 2
120
I
40
0 20 40 60 80
a, MPa Fig. 4. Variation of the gliding lines lengthes L wit
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