B. Johs

Ellipsometric determination of optical constants for silicon and thermally grown silicon dioxide via a multi-sample, multi-wavelength, multi-angle investigation

Optical constant spectra for silicon and thermally grown silicon dioxide have been simultaneously determined using variable angle of incidence spectroscopic ellipsometry from 0.75 to 6.5 eV. Spectroscopic ellipsometric data sets acquired at multiple angles of incidence from seven samples with oxide thicknesses from 2 to 350 nm were analyzed using a self-contained multi-sample technique to obtain Kramers–Kronig consistent optical constant spectra. The investigation used a systematic approach utilizing optical models of increasing complexity in order to investigate the need for fitting the thermal SiO2 optical constants and including an interface layer between the silicon and SiO2 in modeling the data. A detailed study was made of parameter correlation effects involving the optical constants used for the interface layer. The resulting thermal silicon dioxide optical constants were shown to be independent of the precise substrate model used, and were found to be approximately 0.4% higher in index than publis...

InP optical constants between 0.75 and 5.0 eV determined by variable‐angle spectroscopic ellipsometry

Using variable‐angle spectroscopic ellipsometry (VASE) InP optical constants for photon energies have been determined in the range from 0.75 to 5.0 eV, which includes the fundamental gap at 1.35 eV. Above 1.5 eV the results are consistent with previously measured pseudovalues from an oxide‐stripped sample when a very thin residual overlayer is accounted for. They are also shown to be compatible with previously published prism measurements of refractive index below the band gap. Real and imaginary parts of the dielectric function are shown to be Kramers–Kronig (KK) self‐consistent above the gap, and the KK analysis was used to extend the dielectric function below the measurement range to 0.5 eV. The assumptions underlying biased fitting of VASE data and the importance of variable‐angle measurements were investigated. The detection and significance of systematic errors for general VASE data analysis were also investigated, especially with regard to fit parameter confidence limits.

Determination of AlAs optical constants by variable angle spectroscopic ellipsometry and a multisample analysis

Using variable angle spectroscopic ellipsometry, optical constants for AlAs (1.4–5.0 eV) are presented which are simultaneously compatible with measured data from four different samples. The below‐gap index values are compatible with published prism measured values. The second derivative spectrum are compatible with published values above the direct band gap. The AlAs spectra is Kramers–Kronig self‐consistent over the measured range and is compatible with published values from 0.6 to 1.4 eV. The optical constants for thin (<50 A) GaAs caps on AlAs are shown to be different from bulk GaAs values and require special consideration when fitting ellipsometric data. For the thin GaAs caps, the E1 and E1+Δ1 critical‐point structure is shifted to higher energies as previously observed for GaAs quantum wells. Bulk AlAs optical constants are shown to be different from those of a thin (∼20 A) AlAs barrier layer embedded in GaAs. The thin barrier layer exhibits a highly broadened critical‐point structure. This barrie...

Studies of thin strained InAs, AlAs, and AlSb layers by spectroscopic ellipsometry

The optical constants for thin layers of strained InAs, AlAs, and AlSb have been investigated by spectroscopic ellipsometry and multi‐sample analyses. These materials are important for high‐speed resonant tunneling diodes in the AlAs/InAs/In0.53Ga0.47As and AlSb/InAs material systems. Understanding the optical properties for these thin layers is important for developing in situ growth control using spectroscopic ellipsometry. Ex situ room‐temperature measurements were made on multiple samples. The resulting fitted optical constants are interpreted as apparent values because they are dependent on the fit model and sample structure. These apparent optical constants for very thin layers can be dependent on thickness and surrounding material, and are generally applicable only for layers found in a similar structural context. The critical point features of optical constants for the strained layers and for the thin unstrained cap layers were found to differ from bulk values, and three principle effects (strain, quantum confinement, and thin‐barrier critical‐point broadening) have been identified as responsible. Of these three, the broadening of the E1 and E1+Δ1 critical points for thin barrier material is the newest and most pronounced. This thin barrier effect is shown to be a separate effect from strain, and is also observable for the AlAs/GaAs system.The optical constants for thin layers of strained InAs, AlAs, and AlSb have been investigated by spectroscopic ellipsometry and multi‐sample analyses. These materials are important for high‐speed resonant tunneling diodes in the AlAs/InAs/In0.53Ga0.47As and AlSb/InAs material systems. Understanding the optical properties for these thin layers is important for developing in situ growth control using spectroscopic ellipsometry. Ex situ room‐temperature measurements were made on multiple samples. The resulting fitted optical constants are interpreted as apparent values because they are dependent on the fit model and sample structure. These apparent optical constants for very thin layers can be dependent on thickness and surrounding material, and are generally applicable only for layers found in a similar structural context. The critical point features of optical constants for the strained layers and for the thin unstrained cap layers were found to differ from bulk values, and three principle effects (strain,...

Spectroscopic ellipsometry studies of indium tin oxide and other flat panel display multilayer materials

Abstract Variable angle of incidence spectroscopic ellipsometry (VASE®) ∗ is a rapid and powerful non-destructive optical technique often used to characterize thin films and multilayered structures. A monochromatic, linearly polarized beam of light is reflected from a sample surface at a known angle of incidence, and the resulting polarization state of the reflected beam is measured as a function of wavelength and angle of incidence. Acquired data are then used to determine the optical constants, film thicknesses, and other parameters in the assumed model for the sample. The VASE ® experiment is particularly useful for the characterization of materials for flat panel displays. In the present work, we demonstrate the use of VASE ® on several specific materials for display applications: conducting indium tin oxide (ITO), hydrogenated amorphous silicon, and silicon dioxide, all deposited onto glass substrates.

In situ spectroscopic ellipsometry in molecular beam epitaxy

Noninvasive, real‐time material growth monitoring is becoming increasingly important as epitaxial layer structures become more complex and the thickness and alloy composition tolerances are reduced. The technique of spectroscopic ellipsometry has been adapted to a commercial III–V semiconductor molecular beam epitaxy (MBE) system to monitor layer thickness, ternary alloy composition, and substrate temperature in real time during the growth of multilayer structures. Practical system considerations for reliably implementing the rotating analyzer ellipsometer in a hydride source MBE environment that contains a high pressure of dimeric group V species will be discussed. Measurement of substrate temperature from room temperature to typical growth temperatures will then be presented as well as in situ determination of alloy composition and thickness for efficient growth calibration. A growth run of GaAs/AlGaAs epitaxial layers will be examined to observe surface smoothing upon group III pulse deposition and gro...

Preparation of high Tc Tl‐Ba‐Ca‐Cu‐O thin films by pulsed laser evaporation and Tl2O3 vapor processing

Tl‐Ba‐Ca‐Cu‐O superconducting thin films with zero‐resistance temperatures up to 115 K have been prepared using a Tl2 O3 vapor process on Ba‐Ca‐Cu‐O precursor thin films. The Ba‐Ca‐Cu‐O thin films were made by laser deposition on Y‐stabilized ZrO2 substrates. This technique minimizes problems caused by the toxicity of Tl2 O3, and its subsequent decomposition to the volatile and toxic Tl2 O upon heating. Therefore, it may have practical application in the fabrication of high Tc Tl‐Ba‐Ca‐Cu‐O superconducting thin‐film devices.

Preparation of high T/sub c/ Tl-Ba-Ca-Cu-O thin films by pulsed laser evaporation and Tl/sub 2/O/sub 3/ vapor processing

Tl‐Ba‐Ca‐Cu‐O superconducting thin films with zero‐resistance temperatures up to 115 K have been prepared using a Tl2 O3 vapor process on Ba‐Ca‐Cu‐O precursor thin films. The Ba‐Ca‐Cu‐O thin films were made by laser deposition on Y‐stabilized ZrO2 substrates. This technique minimizes problems caused by the toxicity of Tl2 O3, and its subsequent decomposition to the volatile and toxic Tl2 O upon heating. Therefore, it may have practical application in the fabrication of high Tc Tl‐Ba‐Ca‐Cu‐O superconducting thin‐film devices.

Highly oriented Tl2Ba2Ca2Cu3O10 thin films by pulsed laser evaporation

We have fabricated superconducting thin films on MgO(100) substrates with nearly pure Tl2Ba2Ca2Cu3O10 (2:2:2:3) phase using pulsed laser evaporation and post‐annealing. The films had c axes perpendicular to the substrates. Superconducting films with onset temperatures of 125 K and zero resistance at 110 K were obtained. X‐ray microprobe fluorescence measurements indicate that a typical composition of films is Tl0.66Ba1.77Ca1.46Cu3Ox, which is low in Tl compared to that expected for the 2:2:2:3 phase. A typical grain size is greater than 10 μm as revealed by scanning electron microscopy.

In-situ spectroscopic ellipsometry of HgCdTe

An in-situ spectroscopic ellipsometer has been equipped on a molecular beam epitaxy system to improve control of HgCdTe growth. Using this device, in-situ analysis of composition, growth rate, and surface cleanliness were monitored. A real time model which determined the compositional profile was used. The ellipsometer was employed to give in-situ real time control of the growth process.