John W Little

US Patent:

50478222, Sep 10, 1991

Filed:

Mar 24, 1988

Appl. No.:

7/172518

Inventors:

John W. Little - Wheaton MD
Richard P. Leavitt - Silver Spring MD

Assignee:

Martin Marietta Corporation - Bethesda MD

International Classification:

H01L 2714
H01L 3100

US Classification:

357 30

Abstract:

A quantum well semiconductor device that is responsive to optical energy and operates by resonant field ionization of quantum confined excitons and comprises a semiconductor device including a multi-layered semiconductor structure fabricated on the substrate and including at least two quantum well layers of mutually different widths separated from each other by a semiconductor barrier layer. Because of the different widths, the two quantum well layers have distinct and different electron and hole sub-band energies which when an external electric field is applied across the semiconductor structure, it is possible to bring the electron sub-bands of the wells into resonance, whereupon electrons tunnel back and forth through the barrier layer thereby altering the light absorption coefficient near the excitonic absorption feature. This mechanism provides a means to phase shift or modulate the light traversing through the device.

US Patent:

55195296, May 21, 1996

Filed:

Feb 9, 1994

Appl. No.:

8/193979

Inventors:

John S. Ahearn - Sykesville MD
John W. Little - Ellicott City MD

Assignee:

Martin Marietta Corporation - Bethesda MD

International Classification:

G02F 103

US Classification:

359248

Abstract:

A device for converting a mid-wave infrared or long-wave infrared thermal image into a coherent near-infrared image includes a two-dimensional array of quantum-well-based optical modulators and infrared photodetectors. Each modulator is integrated or hybridized with a respective photodetector, and the combination is connected to an electronic circuit. Variations in mid-IR or long-IR light intensity are converted by each photodetector into variations in a bias applied to its respective modulator. The bias variations modulate the intensity and/or phase of near-IR light illuminating the modulators.

US Patent:

59658991, Oct 12, 1999

Filed:

Sep 1, 1994

Appl. No.:

8/300097

Inventors:

John W. Little - Ellicott City MD

Assignee:

Lockheed Martin Corp. - Nashua NH

International Classification:

H01L 2915

US Classification:

257 17

Abstract:

A semiconductor device for detecting radiation includes a plurality of quantum well layers, each of which has bound ground and excited states, interleaved with a plurality of superlattice barrier layers, each of which has a miniband of energy states. By selection of the thicknesses and compositions of the layers, the excited states of the quantum wells have energies that are approximately equal to energies of states in the minibands. Thus, the excited states and minibands form a band of energy states that is substantially continuous across the pluralities of layers. Carriers are excited from the quantum wells' ground states to the excited states by photon absorption and are swept into and through the minibands by an externally applied electric field. The carriers are collected as photocurrent. The excited states may be selectively positioned in the minibands to tailor the properties of the devices, which can have both n-type and p-type dopants.

US Patent:

20190036473, Jan 31, 2019

Filed:

Sep 21, 2017

Appl. No.:

15/710947

Inventors:

- Adelphi MD, US
Andrei V. Sergeyev - Silver Spring MD, US
John W. Little - Ellicott City MD, US

International Classification:

H02S 10/30
H01L 31/054
H01L 31/056
G02B 5/28
G02B 1/115

Abstract:

Embodiments of the invention generally relates to photovoltaic, thermophotovoltaic, and laser power beaming devices which convert solar light, thermal radiation, or laser radiation into electric power. Said devices have a reflective interference “greenhouse” filter placed in front of a semiconductor cell and a reflective mirror on the back of the cell. The front filter is transparent for high energy (short wavelength) photons, but traps low energy (long wavelength) photons emitted by photocarriers accumulated near the semiconductor bandgap. In the optimized PV device, the chemical potential of photoelectrons near semiconductor bandgap exceeds the chemical potential of photoelectrons above the photonic bandgap established by the filter (i.e., the device is in chemical nonequilibrium). The greenhouse filter reduces the emission losses, decreases the semiconductor cell thickness, and provides PV conversion with reduced nonradiative losses. Said device converts radiative energy into electricity in a more efficient way than conventional cells.