Effective electron-density variation and atomic configuration of Al inAlxGa1−xAs

The nuclear magnetic resonance spectrum of ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ in ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As was measured for various AlAs contents. The resonance line shifted to a lower magnetic field as the AlAs content decreased. This chemical shift is interpreted as being caused by a variation in the effective electron density on Al, and suggests that the strength of the Al—As bond decreases with decreasing AlAs content. The decrease of the effective electron density of Al was estimated to be 0.03 when the AlAs content was decreased from 1 to near zero. An additional broader peak was observed for highly doped ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As. The position of this peak was essentially constant with the variation of AlAs content and of the polarity of the sample. The origin of the additional peak was tentatively assigned to the nontetrahedral configuration of As bonding to Al.