Raman scattering study of coupled hole-plasmon–LO-phonon modes in p-type GaAs and p-type ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As

The hole-plasmon–LO-phonon coupling has been studied with the use of Raman scattering from Be-doped p-type GaAs and p-type ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As layers grown by molecular-beam epitaxy. The Raman spectra from heavily doped (100) p-type GaAs layers show a shoulder and a broad peak on the higher- and lower-frequency sides of the LO-phonon peaks, respectively. The structures on both sides of the LO-phonon peaks are assigned to the coupled hole-plasmon–LO-phonon modes by their frequencies and dampings which are dependent on the hole concentration and by comparison with the spectra from (110) cleaved surfaces. In the Raman spectra from (100) p-type ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As layers with high hole concentrations, three modes in addition to two LO-phonon branches are observed; they are identified as branches of the coupled modes by comparison with the Raman spectra of p-type GaAs layers, with reference to experimental results for n-type ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As layers. The coupling between single-particle hole excitations and TO phonons is also discussed for the spectra from the (110) surfaces of p-type GaAs with different hole concentrations.