US 8,300,227 B2Granted

Method and apparatus of z-scan photoreflectance characterization

AssigneeXitronix Corporation

InventorWilliam W. Chism, II

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Abstract

A method of z-scan photo-reflectance characterization of semiconductor structures and apparatus for same has been developed. The method and apparatus provides the ability to independently measure electro-refractive and electro-absorptive nonlinearities that occur in conventional photo-reflectance signals. By performing a series of photo-reflectance measurements, each containing photo-modulated nonlinear optical signals, with the sample at a multiplicity of positions along the focal length of the probe light column, and with an aperture fixtured in the reflected probe path, precision characterization of both electro-refractive and electro-absorptive nonlinearities is attained. The Z-scan photo-reflectance method and apparatus characterizes spatial distortions of a coherent photo-reflectance probe light beam due to electro-refractive and electro-absorptive effects.

Claims20

Dependent claims

A method of z-scan photo-reflectance characterization of a semiconductor structure, the method comprising the steps of:

(a) illuminating an area of a surface of the semiconductor structure using an amplitude modulated pump laser beam, wherein
(i) the pump laser beam comprises at least one wavelength with energy greater than the smallest interband transition energy of a semiconductor material within the semiconductor structure, thereby inducing time periodic changes in electronic charge density within the semiconductor structure such that the electric field profile within the semiconductor structure obtains a time periodic modulation, and
(ii) the semiconductor material within the semiconductor structure is subject to a time periodic modulation of interband transition energies;
(b) illuminating a portion of said modulated electric field profile of step (a) with a separate probe laser beam, wherein the probe laser beam comprises at least one wavelength
(i) nearby an interband transition energy of the semiconductor material within the semiconductor structure, and
(ii) suitable for recording the induced changes in semiconductor material optical response which occur nearby to interband transition energies;
(c) recording reflected alternating current probe light from the illumination of the semiconductor structure, wherein the alternating current probe light comprises a photo-reflectance signal;
(d) performing a series of photo-reflectance measurements of steps (a), (b), and (c), with the semiconductor structure at a multiplicity of positions along the focal length of the probe light column, wherein an aperture is fixtured in the far field of the probe laser beam;
(e) using the information collected in steps (a), (b), (c), and (d) to determine a physical property of the semiconductor structure, including at least one of a nonlinear refraction or a nonlinear absorption.

6 more elements

An apparatus for detecting physical properties of a semiconductor structure, comprising:

(a) a pump laser system, wherein the pump laser system is operable
(i) to provide an amplitude modulated laser beam with a modulation frequency in the range of 100 kHz to 50 MHz,
(ii) to operate at optical powers of at least about approximately 5 mW, and
(iii) to contain at least one wavelength with energy greater than the smallest interband transition energy of a semiconductor material within the semiconductor structure;
(b) a probe laser system, wherein the probe laser system is operable
(i) to provide a continuous wave laser beam,
(ii) to operate at optical powers of at most about approximately 15 mW, and
(iii) to contain at least one wavelength nearby an interband transition energy of a semiconductor material within the semiconductor structure;
(c) a photoreceiver operable to generate an electrical current proportional to input intensity;
(d) an optical system, wherein the optical system is operable
(i) to focus at least one of the amplitude modulated laser beam and the continuous wave laser beam onto a common focal position on a surface of the semiconductor structure of diameter at most 50 microns,
(ii) to translate the common focal position through a distance of approximately 10 times the Rayleigh range of at least one of the amplitude modulated laser beam and the continuous wave laser beam, and
(iii) to separate and direct probe light reflected from the semiconductor structure through an aperture fixtured in a far field of the continuous wave laser beam and into the photoreceiver;
(e) a phase locked signal detection system operable to record output of the photoreceiver;
and
(f) a computer comprising measurement and system control software.

13 more elements

Dependencies are inferred from the claim text.

Facts

Application: 12/866,695Filed 13 Feb 2009 · us provisional application
Priority: 13 Feb 2008
Published: US 2010/0315646 A116 Dec 2010
Granted: 30 Oct 2012
Term ends: Not estimatedThe source records don’t support an estimate.

Classification5 codes

G01N 21/55
Systems in which incident light is modified in accordance with the properties of the material investigated: specular reflectivity
H10P 74/207
Characterised by the properties tested or measured, e.g. structural or electrical properties: electrical properties, e.g. testing or measuring of…
G01N 2021/1725
With a modulation of one or more physical properties of the sample during the optical investigation, e.g. electro-reflectance: modulation of…
G01N
Investigating or analysing materials by determining their chemical or physical properties