EXCITONIC PROPERTIES IN (111)B-GROWN (IN,GA)AS GAAS PIEZOELECTRIC MULTIPLE-QUANTUM WELLS/

The excitonic properties in two (111)B-grown In0.15Ga0.85As multiple q uantum well p-i-n diodes, with 7 and 14 quantum wells, respectively, a re investigated by thermally detected optical absorption (TDOA) and by electroreflectance (ER) as a function of applied bias, the latter mod ifying the electric-field distribution in the heterostructure. The lin e shapes of the ER signals are analyzed by means of a multilayer model enabling the energies and the oscillator strengths of excitons to be deduced while the direct measurements of the energy positions of the T DOA peaks provide an accurate determination of the excitonic transitio n energies at zero-voltage applied bias. The excitonic characteristics are calculated by using a variational approach with a two-parameter t rial function. The piezoelectric field in the strained InxGa1-xAs laye rs is determined by including the excitonic contribution. The theoreti cal oscillator strengths are compared to those obtained from ER experi ments for several excitonic transitions; all the physical trends are w ell reproduced but it appears that a quantitative agreement cannot be found without taking into account the in-plane valence-band mixing. A study is also presented for the optimization of optoelectronic devices by means of a figure of merit that combines the oscillator strength o f the fundamental excitonic transition and the ability for such device s to produce the largest energy shift for a l-V additional applied bia s.