Free-exciton transitions in the optical absorption spectra of Ga As 1 − x P x </mml…
1976; American Physical Society; Volume: 13; Issue: 12 Linguagem: Inglês
10.1103/physrevb.13.5415
ISSN0556-2805
AutoresR. J. Nelson, N. Holonyak, W. O. Groves,
Tópico(s)Chalcogenide Semiconductor Thin Films
ResumoOptical-absorption data are presented on thin (\ensuremath{\sim} 2 \ensuremath{\mu}m) $\mathrm{Ga}{\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{P}}_{x}$ samples in the composition range $0.29\ensuremath{\lesssim}x\ensuremath{\lesssim}0.43$, showing a distinct free-exciton absorption peak. In a particularly lightly doped $x\ensuremath{\approx}0.37$ sample (${n}_{d}\ensuremath{\lesssim}7\ifmmode\times\else\texttimes\fi{}{10}^{14}$ ${\mathrm{cm}}^{\ensuremath{-}3}$), the $n=1,2$ free-exciton transitions are resolved at 4.2\ifmmode^\circ\else\textdegree\fi{}K. At 4.2\ifmmode^\circ\else\textdegree\fi{}K the $n=1$ peak shows a broadening \ensuremath{\lesssim} 1 meV, confirming that the band edges in semiconductor alloys are well defined in spite of alloy (As-P) disorder. The observed energy separation ($\ensuremath{\Delta}E\ensuremath{\sim}3.6$ meV) for the $n=1,2$ exciton states gives the value ${E}_{\mathrm{ex}}=4.8$ meV (compared to 4.2 meV in GaAs) for the exciton binding energy in $\mathrm{Ga}{\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{P}}_{x}$ ($x=0.37$). Using the absorption data for these samples, we obtain reliable values for the direct band gap, the band-edge bowing parameter, and the direct-indirect crossover in $\mathrm{Ga}{\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{P}}_{x}$ (${x}_{c}\ensuremath{\approx}0.45,77$ \ifmmode^\circ\else\textdegree\fi{}K).
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