PIEZOELECTRIC EFFECTS IN IL-VI HETEROSTRUCTURES

Large built-in piezoelectric fields are observed in strained CdTe quan tum wells grown along a polar axis with CdZnTe or CdMnTe barriers. Pho toluminescence and absorption spectra give direct evidence of the prog ressive spatial separation of electrons and holes when the electric fi eld increases (i.e., when the misfit strain increases) and when the qu antum well thickness increases: the lines rapidly shift to the red, th e e(1)-h(1) oscillator strength decreases while the e(1)-h(2) one incr eases. The observed redshift allows one to measure the built-in field for different compositions of the barrier (CdMnTe or CdZnTe) and the q uantum well (CdTe or CdZnTe). Significant nonlinearity is found. Such structures are expected to have interesting applications in electro-op tics or non-linear optics. However, their electronic properties result from a balance between the confinement due to band offsets, which ten ds to enhance excitonic effects, and the built-in field, which tends t o separate the electron-hole pair leading to reduced oscillator streng th. By suitably choosing the parameters of the heterostructure, and wi th a good control of growth, multiple quantum wells are realized which exhibit both intense narrow absorption lines and a sizable redshift.