K. Haberland

Real-time monitoring of MOVPE device growth by reflectance anisotropy spectroscopy and related optical techniques

Abstract Reflectance anisotropy spectroscopy (RAS/RDS) so far has been mostly used for basic growth studies in both molecular beam epitaxy (MBE) and metal-organic vapor-phase epitaxy (MOVPE). Due to its sensitivity to the uppermost atomic monolayers, RAS became a very versatile tool for investigating surface stoichiometry, surface reconstruction and surface morphology especially under gas-phase conditions. Meanwhile, however, the performance and adaptability of RAS to standard MOVPE systems has been enhanced significantly and RAS sensors now can also be used for MOVPE device growth monitoring and control. Therefore, after a brief introduction to the basic surface physics and surface chemistry causing the optical signatures, this paper concentrates on device related applications. Examples will be given concerning the optical response to both n-type and p-type GaAs doping levels and the real-time measurement of ternary compound composition for reaching lattice matched growth. The optical surface response during the growth of a complete GaAs/InGaP heterojunction bipolar transistor is visualized. The result indicates on a monolayer level either consistency or deviation from the intended growth process.

Real-time calibration of wafer temperature, growth rate and composition by optical in-situ techniques during AlxGa1−xAs growth in MOVPE

In this paper we report a novel technique, based on optical measurements, to measure the true temperature of the wafer surface during epitaxial growth. It will be shown that this temperature can deviate considerably from the susceptor temperature measured with thermocouples or pyrometers. For this purpose we employed combined in-situ reflectance anisotropy spectroscopy and spectroscopic reflectance measurements in a number of different metal-organic vapor phase epitaxy (MOVPE) reactors. Measurements have been performed on rotating and non-rotating samples during growth of GaAs, AlAs and AlxGa1� xAs. We demonstrate that in a single growth run the reading of a conventional thermocouple can be calibrated to the true wafer temperature, the growth rate can be determined and process calibration for the AlGaAs composition can be established. r 2002 Elsevier Science B.V. All rights reserved.

Ellipsometric and reflectance-anisotropy measurements on rotating samples

Abstract Device grade semiconductor epitaxial growth is usually performed on rotating substrates in order to achieve and composition uniform layer thickness. This often complicates in-situ optical measurements for growth control. Therefore, in this paper we present a method that significantly reduces the signal distortions imposed on RAS (reflectance anisotropy spectroscopy) and ellipsometry spectra by rotating and wobbling samples. Several cases (phase and frequency of the sample rotation either known or unknown, wobbling and ideally rotating samples) are investigated and the respective optimized experimental set-ups are presented for both RAS and ellipsometry.

GaAs cap layer growth and In-segregation effects on self-assembled InAs-quantum dots monitored by optical techniques

The overgrowth of InAs islands by a GaAs cap layer has been investigated by optical in situ measurements at various growth conditions. A better smoothing of the surface has been found for low growth rates. This effect is attributed to a larger diffusion length of the gallium during growth leading to a smoother final surface. The status of the surface during and after cap layer growth can be determined from RAS and SE measurements during growth. This correlation between the optical data and the surface morphology was confirmed by ex situ AFM measurements. Post growth annealing of samples with different cap layer thickness showed indium interdiffusion from the islands to the cap layer over several nanometers. This effect is also observed during cap layer growth at higher temperatures and can be attributed to indium segregation during growth.

In-situ determination of interface roughness in MOVPE-grown visible VCSELs by reflectance spectroscopy

Abstract This paper reports on an in-situ optical reflectance study of the development of the interface roughness of AlGaAs/AlAs distributed Bragg reflectors during the metalorganic vapour phase epitaxy growth of visible vertical-cavity surface-emitting laser structures. We show that the surface roughness can be extracted from time-resolved UV reflectance measurements. The roughness of the surface during growth for both the AlGaAs and AlAs layers can be determined individually. The values estimated from the in-situ optical data correlate well with the roughness measured ex-situ using atomic force microscopy. The in-situ reflectance measurement is thus shown to be a convenient non-invasive and non-destructive technique for determining surface and interface roughness even for complex device structures.