You-Hua Qian

Design of a scanning ellipsometer by synchronous rotation of the polarizer and analyzer

We have designed and constructed a new type of spectroscopic ellipsometer to study the optical properties of materials in the 3500-8000-Å wavelength range. In the system, the analyzer and polarizer are driven 10(4) steps/revolution by two stepping motors that have hollow shafts and rotate synchronously with a speed ratio of 2:1, i.e., A = 2P. Both the polarizer and analyzer are mounted directly on the shafts to avoid mechanical transmission and vibration problems entirely and make the system simple and reliable. An additional source polarizer was placed in the optical path to reduce the slight polarization effects of the light source. The light intensity finally received by the detector contained five components, one dc and four ac, with frequencies of ω(0), 2ω(0), 3ω(0), and 4ω(0), respectively. One can independently obtain the ellipsometric parameters of ψ and Δ as well as the optical constants by calculating any one of the two sets of ac signals, with a raw data self-consistency of better than 0.5%. The incident angle, aligned precisely by a laser beam, was continuously variable through a mechanical system with a computercontrolled resolution of 0.001° or a visual resolution of 0.005°. The system operations, including data acquisition and reduction, high-voltage control of the photomultiplier, incident angle, as well as wavelength setting and scanning, were fully and automatically controlled by a 386-based microcomputer. We self-calibrated the system by adjusting and setting precisely the initial azimuthal angles of the prisms. The results from the measured spectra of the complex refractive index for a gold-film sample are presented, and we show that the data obtained at three different incident angles of 65°, 70°, and 75° are remarkably consistent with one another. A comparison of the two results from the ellipsometry and reflectance measurements is given. The experimental skills and system error reduction are discussed in detail.

Mechanism of charge generation in p -type doped layer in the connection unit of tandem-type organic light-emitting devices

A p-type doped organic layer combined with a hole-blocking layer has been experimentally demonstrated to serve as the charge generation unit in tandem-type organic light-emitting devices. The p-type layer functions as the source of both holes and electrons. Charge separation is explained by the tunneling model that the hole-blocking layer reduces the energy barrier for the electrons generated in the p-type layer to tunnel through into one light-emitting unit, while the holes generated in the p-type layer can transport to the other light-emitting unit easily under operation voltage.

Method to measure spectra of both the magneto-optical Kerr and the Faraday effect

Details of an integrated apparatus to measure spectra of both the magneto-optical Kerr and the Faraday effect by the use of a rotating analyzer are given. The absolute values of both the Kerr rotation angle theta(k) and the ellipticity epsilon(k) can be determined by means of an achromatic quarter-wavelength retarder. The system is simple and reliable, and fully controlled by a computer. The measured values of the Kerr and Faraday effects for one MnBi(Al) film sample and for one GaP crystal sample are given. Since the magnitude of the Faraday rotation signal is proportional to the sample thickness, one must be careful in determining the fundamental energy gap by use of the Faraday spectrum only. Employment of the Fourier-transform technique will enable the system to measure both the Kerr and the Faraday effect in a wider data range from one-hundredth to a few hundred degrees

Oscillations of interlayer coupling and magneto‐optics in sputtered Co–Al/Cu multilayers

We have prepared [Co90Al10/Cu]30 multilayers by ion beam sputtering and studied the behavior of interlayer coupling, magnetoresistance, and the magneto‐optical Kerr effect. For Co–Al/Cu multilayers, the in‐plane saturation field, coercive force HC and magnetoresistance ratio ΔR/R have been observed to oscillate with a period of about 0.9 nm, as a function of Cu spacer layer thickness. Furthermore, polar Kerr rotation θk in visible wavelength range also oscillates with the same period. The magneto‐optical activities may be attributed to changes in the optical constants with the magnetic state.

Disorder activated optical modes and the phonon dispersion of AlxGa1−xAs lattice vibration

Abstract The resonant Raman and polarization behavior were measured for ternary compound Al 0.7 Ga 0.3 As prepared by molecular beam epitaxy. A one dimensional linear chain model is proposed to calculate the behavior of short wavelength optical phonons. By using the concept of random element isoamplitude instead of random element isodisplacement and by using a pair of asymmetric effective force constants to describe the total effect to polarized field and short range interaction, the calculated results fit well the data. The observed disorder activated optical modes are attributed to the optical phonons at the Brillouin zone edges.

Ferromagnetic resonance study of Co/Pt multilayers

Abstract In this paper the results of ferromagnetic resonance study of sputtered Co/Pt multilayers, with a fixed Co layer thickness of 15 A, are presented. For these multilayers with small Pt layer thickness, in addition to a uniform resonance mode, a spin wave resonance mode is found to exist, which confirms the existence of an interlayer coupling between the neighboring Co layers. Simultaneously, the effective magnetization 4πMeff and the resonance linewidth ΔH are found to change correlatively with varying Pt layer thickness. This phenomenon can be explained as a result of an interplay between the interlayer coupling and the low-dimensional effect.

Study of apparent Faraday rotation of an optically anisotropic system

We present a formula which can be used to analyze the anisotropic and apparent Faraday effect occurring in a material having an optically anisotropic property. By using the formula the real Faraday parameter can be obtained. For example, we have used the formula to study the anisotropic Faraday effect of a single‐crystal Cd0.55Mn0.45Te measured with the spectroscopic ellipsometer and rotating‐analyzer‐type Kerr apparatus. The calculated data were in good agreement with the experimental results.

Magnetic and magneto‐optical properties of multilayers Fe‐Si/Pd

The magnetic and magneto‐optical properties of Fe‐Si/Pd multilayers prepared by rf sputtering were studied. For Fe‐Si/Pd multilayers with a fixed Fe‐Si layer thickness dm of 15 A and the Pd layer thickness dp increasing from 10.8 to 18 A, the saturation magnetization Ms and the Kerr rotation θk decrease sharply and reach a minimum. With dp further increasing, the multilayers increase. Ms is almost constant and θk decreases slightly when dp≳36 A. For Fe‐Si/Pd (54 A) multilayers the room temperature Ms decreases and θk increases, respectively, with increasing dm. This is caused by the spin‐polarization effect of Pd atoms near the interfaces.

New design to measure absolute spectral reflectivity

A new type of normal incidence scanning reflectometer is designed and constructed. In the system design, instead of using a reference reflective sample or the optical path adjustment methods as in traditional design, we use a fused quartz M-type prism to split the beam of incidence light into two beams in a total internal reflection configuration. The spot sizes, intensities, and spectral responses of these two light beams, therefore, are identical. One reference beam goes directly to the detector. Another sampling beam goes to the sample and is measured by the same detector after beam reflection. A metal disk having three holes is driven precisely by a stepping motor and is used to control the reference and reflection beams as well as the background signals, which are measured in sequence. In terms of the three signals, the absolute reflectivity of the sample at a certain wavelength can be determined immediately using the computer. The system is controlled automatically by the computer with a working wavelength range from 400 to 800 nm. The incidence angle is fixed and equals about 5 deg. The details of the system design, optical configuration, and error reduction are given and discussed. The measured spectral results of the reflectivity for a few testing samples are also given, and are shown to be in good agreement with those measured by other optical methods. The designed system, however, is simpler and can be used in many optical studies.

CHARACTERISTICS OF HIGH-ENERGY N+-IMPLANTED DAMAGE IN GASB

Abstract Characteristics of 2 MeV N+-implanted damage in GaSb samples with doses from 1 × 1013 cm−2 to 1 × 1015 cm−2 were studied by use of spectroscopic ellipsometry, Rutherford backscattering spectrometry in combination with the channeling technique, and scanning electron microscopy methods. When doses are greater than 3 × 1014 cm−2, the implanted layer becomes amorphous. But no swelling was observed on the implanted sample surfaces, as predicted by R. Callec. By rapid thermal annealing at 600°C for 25 s, a good recovery of the implanted layers has been achieved.