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PHOTOCONDUCTING PULSE GENERATOR OF GaAs WITH PICOSECOND RESPONSE

IP.com Disclosure Number: IPCOM000043338D
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Kash, JA: AUTHOR

Abstract

In measuring the response of ultrafast electronic devices, the principal difficulty is the propagation of the picosecond electrical pulses from the pulse generating photoconductor to the device under study, and from there to the sampling photoconductor. A monolithic approach in which the photoconductive elements are fabricated on the same substrate as the device to be tested will eliminate the difficulties inherent in the propagation of picosecond electrical pulses through discrete circuit elements. The fastest devices now fabricated are produced using GaAs and GaAlAs made by molecular beam epitaxy (MBE). The photoconductive pulse generator is shown in the figure, and the photoconductive sampler is identical thereto except for the electrical connections, as are described in the figure caption.

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PHOTOCONDUCTING PULSE GENERATOR OF GaAs WITH PICOSECOND RESPONSE

In measuring the response of ultrafast electronic devices, the principal difficulty is the propagation of the picosecond electrical pulses from the pulse generating photoconductor to the device under study, and from there to the sampling photoconductor. A monolithic approach in which the photoconductive elements are fabricated on the same substrate as the device to be tested will eliminate the difficulties inherent in the propagation of picosecond electrical pulses through discrete circuit elements. The fastest devices now fabricated are produced using GaAs and GaAlAs made by molecular beam epitaxy (MBE). The photoconductive pulse generator is shown in the figure, and the photoconductive sampler is identical thereto except for the electrical connections, as are described in the figure caption. The pulse generator is built as follows: Begin with a GaAs substrate. The properties of the substrate, such as thickness, doping level and resistivity, are not critical. The substrate may also include layers of GaAs or GaAlAs, if necessary, for the fabrication of other devices. Upon the substrate is grown a buffer layer of GaAlAs or AlAs. The only restriction on the aluminum content of the layer is that the band gap in the layer must be larger than the photon energy of the picosecond laser to be used, which is typically about 2.0 eV. This restriction prevents photoconductivity from occurring in the buffer layer. Other than this restriction, the layer may be of arbitrary doping, thickness, etc. The final semiconductor layer is GaAs. Doping of this layer is again not critical. The layer must not, however, be so thick that the botto...