US 5,457,709 AGranted

Unipolar semiconductor laser

AssigneeAT&T IPM Corp.

InventorsFederico Capasso, Alfred Y. Cho, Jerome Faist, Albert L. Hutchinson, Serge Luryi, Carlo Sirtori, Deborah L. Sivco

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Abstract

This application discloses, to the best of our knowledge, the first unipolar laser. An exemplary embodiment of the laser was implemented in the GaInAs/AlInAs system and emits radiation of about 4.2 .mu.m wavelength. Embodiments in other material systems are possible, and the lasers can be readily designed to emit at a predetermined wavelength in a wide spectral region. We have designated the laser the "quantum cascade" (QC) laser. The QC laser comprises a multilayer semiconductor structure that comprises a multiplicity of essentially identical undoper "active" regions, a given active region being separated from an adjoining one by a doped "energy relaxation" region. In a currently preferred embodiment each active region comprises three coupled quantum wells designed to facilitate attainment of population inversion. In the currently preferred embodiment the energy relaxation regions are digitally graded gap regions. However, other energy relaxation regions are possible. The unipolar plasma in a unipolar laser can be manipulated by means of an electric "control" field, facilitating, for instance, beam steering or external control of the modal gain of the laser. Means for accomplishing this are discussed.

Claims20

Dependent claims

An article comprising a unipolar semiconductor laser, said laser comprising

a) a multilayer semiconductor structure that comprises doped semiconductor material of only a first conductivity type;
and
b) means for applying a voltage across said multilayer semiconductor structure;
characterized in that
c) said multilayer structure comprises a multiplicity of essentially identical active regions, a given of said active regions being separated from an adjoining active region by an energy relaxation region;
d) said active region comprises two or more coupled quantum wells, associated with said coupled quantum wells being at least second and third energy states for charge carriers of the first conductivity type, with said third energy state being higher than said second energy state, associated with said energy states being, respectively, second and third wavefunctions, said active region selected to provide reduced spatial overlap between said third and second wavefunctions;
e) said energy relaxation region is selected to provide for substantial energy relaxation of charge carriers of the first given conductivity type in the energy relaxation region when a normal operating voltage is applied, at least some of said charge carriers being introduced into the energy relaxation region from said active region;
and
f) at least some of the charge carriers of the first conductivity type undergo a radiative transition from the third to the second energy state.

6 more elements

Dependencies are inferred from the claim text.