Correlation of Film Quality and Hydrogen NMR Resonance Shifts in a-Si:D,H; a-Ge:D,H; and a-SiGe:D,H
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echo sequence. By 20 K the diamagnetic shift has reached 200 ppm. It is to be noted also that below 40 K a distinct broadening occurs at the base of the residual narrow proton line in Fig. 1. It appears that the 24 kHz line from the 15 sec spectrum at the top of the figure is partially recovered in the short pulse delay (pd) spectra as the proton T 1 for this component decreases with temperature [2] to become comparable to the pulse delay. This component does not shift with decreasing temperature.
Sample H201P H579 H642 H643 H686 H686P H759P H541
Table I Deposition parameters and photoelectronic characterization of amorphous semiconductor samples T, Power Pressure Flow XH 4 Flow D 2 Type (°C) (W/cm2 ) (Torr) (SCCM) (SCCM) 0.95 GeH 4 :1 40 a-SiGe:H,D 225 0.375 SiH 4 :0.6 20 0.20 231 0.030 a-Si:D a-Ge:H,D 151 0.096 0.95 1 40 a-Ge:H,D 301 0.096 0.95 1 40 0.95 1 40 a-Ge:H,D 248 0.096 40 1 0.95 150 0.096 a-Ge:H,D 76 4 0.70 230 0.200 a-Si:H,D 76 4 0.70 230 0.120 a-Si:H,D
r7l17 (cm 2 /V) 6.6 x 10-8 4.8 9.3 2.5 7.0 3.2 1.5 1.6
kHz FIGURE 1.
Proton line shapes at short recovery time in a-Si:HD.
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FIGURE 2. In frequency-reversed spectra the 60 kHz GeD doublet lines do not shift, but the broad central feature is shifted diamagnetically by 25 ppm. Deuteron magnetic resonance (DMR) line shapes at short spin recovery intervals also show the emergence of a diamagnetically shifted broad central resonance component. Figure 2 shows an example of such a spectrum from an a-Ge:H,D film (H 686P) at 4.2 K. To emphasize the shifted fraction the g(w) spectrum has been overlaid with its reverse g(-w) image. The difference appears at the base of the broad central (BC) feature and here corresponds to a 25 ppm diamagnetic shift. It is probable that the diamagnetic proton and deuteron resonance components in Figs. 1 and 2 arise from some of the o-H 2 and p-D 2 molecules trapped in nanovoids within the films. proton (H1541) ii-L----Z ----
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Temperature variations of diamagnetic shifts for broad FIGURE 3. central proton and deuteron spectra.
181
Figure 3 shows the temperature variations of the diamagnetic shifts of the broad central features of the proton and deuteron resonances in high photoelectronic quality a-Si:H,D film (H541) and in a good quality a-Ge:H,D film (H686P). The diamagnetic shifts (of the proton spectra shown in Fig. 1) nearly vary as 1/T. The deuteron shifts show a smaller variation with T, but lie in the same ppm range as the proton shifts. Proton shifts which approximate 1/T variation have been reported [3] to occur at low temperatures in solid H2 . These arise from the I. f spin
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