At&t Bell Laboratories

Bell Telephone Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

Tao-Yuan Chang

Daniel S Chemla

Israel Bar-Joseph

David A Miller

Theodoor Charlouis Damen

Jane E Zucker

Chinlon Lin

Van-Tran Nguyen

Harry W Tom

Rubens Da Miranda

A method for manufacturing a semiconductor device which includes a step of evaluating the dopant profile, in at least the depth dimension, in a processed or partially processed wafer. The evaluation is performed nondestructively, by measuring a differential reflectivity spectrum of the doped portion of the wafer. The resulting spectrum can be related to the Fourier transform of the dopant profile in the depth dimension.

Method for manufacturing a semiconductor device, including optical

Polarization independence and higher intrinsic speed resulting from lowered device capacitance are achieved in a modulation-doped semiconductor heterostructure wherein a transfer barrier region including a graded bandgap semiconductor layer facilitates flow of carriers (electrons) from a doped reservoir to a narrow bandgap active region while an isolation barrier region confines carrier flow to be substantially within the graded bandgap region and the associated active region to minimize leakage current. The present modulation-doped heterostructure exhibits substantially equal end-boundary conditions in an unbiased condition for efficient cascading or stacking with additional modulation-doped heterostructures. Several embodiments of the present invention are described in which grading in the transfer barrier region is shown to include substantially continuous compositional grading, stepwise compositional grading, and superlattice grading. In these embodiments, the thickness of the active region is determined in proportion to the size of the optical effect which is to be produced.

Semiconductor device including cascadable polarization independent

Modulation-doped quantum well heterostructures are cascaded in a semiconductor device to achieve high speed operation while obtaining large index of refraction or absorption coefficient changes for modulating lightwave signals without significant increases in the operating potentials over prior quantum well structures. Each modulation-doped quantum well heterostructure exhibits substantially equal boundary conditions in an unbiased condition for efficient cascading or stacking. Each quantum well has associated with it a barrier layer to minimize leakage current. As a result, each quantum well has associated with it a separate charge reservoir. This aspect contributes to the speed of the cascaded structure. When incorporated within a waveguide structure, cascaded modulation-doped quantum well heterostructures can act as an external modulator, or as an intra-cavity wavelength tuning element, or as an intra-cavity modulator, or even as an optically-pumped laser.

Semiconductor device including cascaded modulation-doped quantum well

Optical apparatus is disclosed wherein narrow line width light from a source is directed through the substrate of a semiconductor structure and reflected from the gate electrode of a field effect transistor element fabricated on the surface of the semiconductor structure. A quantum well layer serves as the current channel for the field effect transistor, and charge carries from a doped semiconductor layer provide high mobility carriers in the quantum well layer. Changes in the potential between the gate and source electrodes of the field effect transistor causes the normal pinchoff of carriers in the quantum well layer thereby causing changes in the absorption characteristic presented by the quantum well layer. By directing light from the source at the gate electrode through the substrate of the semiconductor structure, a photodetector can be positioned so as to detect a change in light which has passed twice through the quantum well layer, thereby detecting a change in the electrical state of the field effect transistor.

Optical reading of quantum well device

Far-infrared tunable radiation is produced in a four-level laser system by using a pumping means for exciting population from the lowest level of the system to the upper level of a laser transition to create a population inversion between the upper and lower levels of the laser transition and a laser beam which is nearly resonant with the lower level of the laser transition and a fourth level of the system. The laser beam shifts the lower level of the laser transition according to the dynamic Stark effect to provide for tuning of the far-infrared radiation.

Far-infrared laser tuned by the dynamic Stark effect

A tunable far infrared generator makes use of a four-photon mixing process that cycles among highly excited atomic states, the lowest of which states is reached from the atomic ground state by a visible or ultraviolet photon, and the remainder of which states are connected by transitions in the infrared.

Generation of tunable far-infrared radiation

The optically pumped submillimeter wave lasers employing molecular gases having dipole moments are improved by employing as a polyatomic buffer gas a molecular gas or vapor of a hydrocarbon having a significantly large vibrational heat capacity in relation to its molecular weight. An example is C.sub.6 H.sub.14 added to such lasers as the methyl fluoride laser at 496 micrometers. Other examples of saturated hydrocarbon buffers are also given; and in each case the vapor molecule is complex enough to absorb many vibrational quanta from the active molecules, yet is small enough to move rapidly to the tube walls.

Growing community of inventors

Lincroft, NJ, United States of America

Tao-Yuan Chang