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Monochromatic High Frequency Ultrasonic Wave Generation

IP.com Disclosure Number: IPCOM000045730D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Chang, LL: AUTHOR [+3]

Abstract

Coherent generation of ultrasonic waves in the far infrared frequency range by electromagnetic radiation may be accomplished in a periodic space-charge layer structure made of semiconductors. The structure is capable of operating at high frequencies without the difficulty of skin-depth effects nor the application of magnetic fields, as in the case of metals.

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Monochromatic High Frequency Ultrasonic Wave Generation

Coherent generation of ultrasonic waves in the far infrared frequency range by electromagnetic radiation may be accomplished in a periodic space-charge layer structure made of semiconductors. The structure is capable of operating at high frequencies without the difficulty of skin-depth effects nor the application of magnetic fields, as in the case of metals.

The active region of the device consists of a one-dimensional periodic structure of semiconductors, or a superlattice, in which positive and negative space-charge layers are present in an alternating fashion, as may be seen in the figure. Examples of such periodic Layers are positively charged donors and free electrons in a GaAs-GaA1As superlattice; free electrons and holes in an InAs- GaSb superlattice; or even carriers in a series of properly designed p-n junctions. A typical period in thickness is in the range of approx. 100-1000 Angstroms. This active region can be grown on a suitable substrate by various epitaxial processes, including molecular beam epitaxy which offers special advantages in terms of thickness and compositional controls.

Along the z-direction perpendicular to the layers, the charge density can be written as Rho (z)=Alpha (z) Sigma(n) Rho (n) exp (2 Phi inz/d), where d is the period, and Alpha (z) is a slowly varying function of z to account for the fact that the active region does not contain an infinite number of periods. In other words, the thickness of the acti...