Optical absorption spectroscopy for semiconductors
First Claim
1. A method for spectroscopically analyzing optical absorption in a semiconductor sample comprising the steps offorming a first cladding layer, a semiconductor sample layer, and a second outer cladding layer on a substrate, said first and second cladding layers having a larger band gap than said sample layer, wherein said sample layer and said first and second cladding layers are all of one conductivity type, and said substrate is of an opposite conductivity type, and wherein a p-n junction between said substrate and said first cladding layer is sensitive to optical radiation at a wavelength above absorption edges of said first and second cladding layers,forming a first electrode structure on said substrate,forming a second electrode structure on said second cladding layer, said second electrode structure being transparent to said optical radiation,directing said optical radiation toward said sample layer through said second cladding layer, andderiving a signal from said first and second electrode structures, said signal being related to a voltage generated across said p-n junction by a photovoltaic effect, and said signal being indicative of optical absorption in said sample layer of incident optical radiation in a wavelength range above said absorption edges of said first and second cladding layers and below a wavelength limit where said p-n junction is sensitive,wherein said second outer cladding layer has a sufficient thickness to prevent a depletion layer from extending into said semiconductor sample layer, said depletion layer being associated with a junction of said second cladding layer and said second electrode structure, and wherein said first cladding layer is sufficiently thick to substantially confine charge carriers generated by absorption of said optical radiation in said semiconductor sample layer.
1 Assignment
0 Petitions
Accused Products
Abstract
Optical absorption data for a semiconductor sample is derived by providing a p-type layer (4) of the semiconductor sample between two larger band gap p-type cladding layers (3,5) on an n-type substrate (1). A p-type buffer layer (2) may be present on the substrate (1). Optical radiation is directed towards the p-n junction (6) between the substrate (1) and the buffer layer (2) through a transparent electrode (8) on the outer cladding layer (5). A further electrode (7) contacts the substrate (1) whereby an electric signal can be derived which is related to the voltage generated by the photovoltaic effect at the p-n junction. This signal is indicative of the absorption in the semiconductor sample (4) of the incident radiation in the wavelength range above the absorption edges of both cladding layers and below the wavelength limit at which the p-n junction is sensitive.
6 Citations
26 Claims
-
1. A method for spectroscopically analyzing optical absorption in a semiconductor sample comprising the steps of
forming a first cladding layer, a semiconductor sample layer, and a second outer cladding layer on a substrate, said first and second cladding layers having a larger band gap than said sample layer, wherein said sample layer and said first and second cladding layers are all of one conductivity type, and said substrate is of an opposite conductivity type, and wherein a p-n junction between said substrate and said first cladding layer is sensitive to optical radiation at a wavelength above absorption edges of said first and second cladding layers, forming a first electrode structure on said substrate, forming a second electrode structure on said second cladding layer, said second electrode structure being transparent to said optical radiation, directing said optical radiation toward said sample layer through said second cladding layer, and deriving a signal from said first and second electrode structures, said signal being related to a voltage generated across said p-n junction by a photovoltaic effect, and said signal being indicative of optical absorption in said sample layer of incident optical radiation in a wavelength range above said absorption edges of said first and second cladding layers and below a wavelength limit where said p-n junction is sensitive, wherein said second outer cladding layer has a sufficient thickness to prevent a depletion layer from extending into said semiconductor sample layer, said depletion layer being associated with a junction of said second cladding layer and said second electrode structure, and wherein said first cladding layer is sufficiently thick to substantially confine charge carriers generated by absorption of said optical radiation in said semiconductor sample layer.
-
13. An apparatus for spectroscopically analyzing optical absorption in a semiconductor sample comprising
a substrate, a first cladding layer on said substrate, a semiconductor sample layer on said first cladding layer, and a second cladding layer on said sample layer, said first and second cladding layers having a larger band gap than said sample layer, wherein said sample layer and said first and second cladding layers are all of one conductivity type, and said substrate is of an opposite conductivity type, and wherein a p-n junction between said substrate and said first cladding layer is sensitive to optical radiation of a wavelength above absorption edges of said first and second cladding layers, first electrode means for contacting said substrate, second electrode means transparent to optical radiation for contacting said second cladding layer, radiation means for directing monochromatic optical radiation to said sample layer through said transparent second electrode means, and first means for deriving a signal from said first and second electrode means, said signal being related to a voltage generated across said p-n junction by a photovoltaic effect, and said signal indicating absorption in said semiconductor sample layer of said optical radiation.
Specification