Fast measurements of photoreflectance spectra by using multi‐channel detector

Abstract

Photoreflectance (PR) measurements were performed on GaAs‐ and GaN‐based structures in the so called ‘bright configuration’ where the sample was illuminated by white light (probing beam) instead of monochromatic light as it takes place in the standard configuration, i.e., so‐called ‘dark configuration’. Within this concept the whole PR spectrum can be measured/processed at the same time using a multi‐channel detector (i.e., CCD camera) instead the phase sensitive lock‐in detection system with the one‐channel detector. In this work PR spectra for Si δ‐doped GaAs structure have been measured using both the CCD detector system as well as the standard lock‐in technique with the one‐channel detector system. GaAs‐related Franz–Keldysh oscillations, which are typical of Si δ‐doped GaAs structure, have been clearly observed in PR spectra measured by using the two detection systems. In addition, the PR system with the CCD detector has been used to measure PR spectra in the UV spectral region for an InGaN/GaN/Al2O3 structure. In this case, PR resonances related to InGaN and GaN band gap absorption have been clearly observed. Using the PR system with CCD detector the time of PR measurements was reduced to few seconds for both GaAs‐ and GaN‐based structures. It shows that the bright configuration of PR set‐up with multi‐channel detection system is very promising and perspective in the fast diagnostic of semiconductor structures. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Real-time reflectance-difference spectroscopy of GaAs molecular beam epitaxy homoepitaxial growth

“…Arguably, this could be done by employing the "bright PR configuration" 31 that calls for the multichannel measurement of two reflectance spectra with and without light excitation, which are subsequently subtracted to shape the PR spectrum. Alternatively, real-time PR spectroscopy could be carried out by an extension of the technique reported in this paper, i.e., by detecting the PR signal with a multichannel detector and multiplexing the detector output signals over the input channel of a single lock-in amplifier.…”

Fast Differential Reflectance Spectroscopy of Semiconductor Structures for Infrared Applications by Using Fourier Transform Spectrometer

“…In order to solve it, the use of a multichannel silicon-based charge-coupled device (CCD) camera detection system instead of a single-channel lock-in amplifier system in the case of near-infrared and UV spectral ranges in typical grating-based experimental configuration has been proposed. 15,16) Unfortunately, this cannot be extended to wavelengths longer than about 2.2 m due to the lack of suitable multichannel detector. The experimental conditions become even more complex in the mid and far infrared due to a very rich spectrum of absorption lines connected with atmospheric gases which strongly affect the measured total spectra of reflectivity or transmission.…”

Spectroscopy of systems with time variable parameters: photoreflectance of GaAs(001) under cesium adsorption

“…These variations distort the measured spectra and, thus, limit the accuracy of the method. A possible solution consists in parallel acquisition of optical spectra by a linear array detector (photodiode array or CCD) at the exit position of a monochromator [8,9]. However, parallel acquisition is not always suitable because of physical and technical reasons.…”

“…It is also difficult to combine the method of parallel acquisition with the lock-in detection technique, which yields a considerable enhancement of the signal-to-noise ratio. For PR spectroscopy an important drawback of using parallel acquisition consists also in the necessity to illuminate the sample with relatively high-intensity white light [9], in contrast to the low-intensity monochromatic illumination in the PR scheme with onechannel registration. High-intensity illumination induces a large surface photovoltage, which, in its turn, flattens the bands at the surface and causes a systematic error in the surface field and band bending determined from the period of FKO.…”