P. Uusimaa

Effects of rapid thermal annealing on strain-compensated GaInNAs/GaAsP quantum well structures and lasers

Strain-compensated GaInNAs/GaAsP quantum well structures and lasers were grown by gas-source molecular beam epitaxy using a rf-plasma nitrogen radical beam source. Effects of rapid thermal annealing on the optical properties of GaInNAs/GaAsP quantum well structures as well as laser diodes were examined. It was found to significantly increase the photoluminescence from the quantum wells and reduce the threshold current density of the lasers, mainly due to a removal of N-induced nonradiative centers from GaInNAs wells.

Molecular beam epitaxy growth of MgZnSSe/ZnSSe Bragg mirrors controlled by in situ optical reflectometry

In situ optical reflectometry at the wavelength of 488 nm was employed to control the growth of MgZnSSe/ZnSSe Bragg mirror stacks for the blue‐green spectral region. 10‐ and 20‐period layer structures of MgZnSSe/ZnSSe were grown on GaAs (100) epilayers by molecular beam epitaxy. A room‐temperature peak reflectance of 86% was obtained for the 20‐period structure at the central wavelength of 474 nm. The results show that, in general, in situ optical monitoring of growth is a viable and simple method for real‐time layer thickness control of MgZnSSe/ZnSSe quarter‐wave stacks.

Structural, electrical, and optical properties of defects in Si-doped GaN grown by molecular-beam epitaxy on hydride vapor phase epitaxy GaN on sapphire

Molecular-beam epitaxy (MBE) has been utilized to grow Si-doped GaN layers on GaN/sapphire templates prepared by hydride vapor phase epitaxy. An extensive set of characterization techniques is applied to investigate the layers. Positron annihilation experiments indicate that the samples contain open volume defects, most likely clusters of vacancies and possibly Ga vacancy-donor complexes. The number of vacancy clusters decreases, as Si concentration is increased. Photoluminescence spectra show that while the absolute intensity of both the yellow and ultraviolet (UV) band-edge transitions increase with Si doping, the intensity ratio of yellow-to-UV emission is decreased. Secondary ion mass spectrometry indicates that the impurity concentrations are in qualitative agreement with the carrier concentrations determined in electrical experiments. The data suggest further that silicon does not affect the diffusion of oxygen. Moreover, transmission electron microscopy reveals that MBE-grown GaN retains the thread...

High-power 600-nm-range lasers grown by solid-source molecular beam epitaxy

This paper presents the performance characteristics and reliability data of AlGaInP-based VISIBLE laser diodes emitting at the wavelengths from 630 to 670 nm. The lasers are grown by toxic gas free solid source molecular beam epitaxy.

Epitaxial lift-off of ZnSe based II-VI structures

The epitaxial lift‐off technique is applied to II–VI based structures. Epilayers of 255 nm thickness containing quantum wells are lifted off their substrates and redeposited onto polyimide coated GaAs. The technique has also been applied to II–VI samples onto which dielectric films had been deposited. Photoluminescence measurements show that the material quality has not been degraded during the processing. The success of this technique with II–VI’s opens up many possibilities for the integration of these materials with metals and dielectrics in vertical structure devices.

Growth and characterization of an epitaxially grown ZnSSe/MnZnSSe distributed Bragg reflector

A Bragg reflector consisting of a 25‐period MnZnSSe/ZnSSE Bragg stack is reported. The II–VI semiconductor structure was grown by molecular beam epitaxy on a GaAs (100) epilayer. Structural characterization of the Bragg reflector was performed with double crystal x‐ray diffraction and transmission electron microscopy. These studies indicated that the epitaxial II–VI structure, whose total thickness is about 2150 nm, remains pseudomorphic with the GaAs substrate. The Bragg stack has a maximum reflectance of 81% at 468 nm. This result shows that fabrication of high reflectance mirrors from epitaxial ZnSe‐based II–VI compounds is possible in spite of relatively small refractive index differences between constituent II–VI layers.

ZNSE/GAAS BAND-ALIGNMENT DETERMINATION BY DEEP LEVEL TRANSIENT SPECTROSCOPY AND PHOTOCURRENT MEASUREMENTS

Using deep level transient spectroscopy and photocurrent measurements we have investigated Schottky contacts formed on p-isotype Zn(SSe)/GaAs heterostructures grown by molecular beam epitaxy on p-GaAs(100) substrates. A deep level located at 0.6 eV above the ZnSe valence band is observed in agreement with literature data for p-type ZnSe, and is used as a reference level for the understanding of photocurrent transitions in the 0.8–3.0 eV energy range. The threshold energies obtained on a series of Zn(SSe)/GaAs samples are explained in terms of absorption processes from the ZnSe and GaAs valence bands, and from the nitrogen acceptor level and a deep level of the ZnSe layers located at 0.1 and 0.6 eV above the valence band maximum, respectively. These absorption processes towards the ZnSe and GaAs conduction bands have been finally used to give the values of the conduction and valence band offsets at p-ZnSe/p-GaAs interface. Our experimental data gives ΔEc=0.25±0.03 eV and ΔEv=1.00±0.05 eV in agreement with ...

Distributed feedback lasers with photon-photon-resonance-enhanced modulation bandwidth

Multi-section distributed-feedback lasers with surface gratings have been fabricated without re-growth by employing ultraviolet nanoimprint lithography. High-frequency photon-photon resonance was exploited to extend the direct modulation bandwidth beyond the conventional limits set by the carrier-photon resonance.

10 Gb/s uncooled dilute-nitride optical transmitters operating at 1.3 µm

Dilute-nitride lasers with record performances have been used to build uncooled transceivers and failure free 10 Gb/s optical transmission was achieved over 815 m of multimode Corning InfiniCor fiber under the LRM standard.

Diffusion of Pt in molecular beam epitaxy grown ZnSe

Diffusion of platinum in zinc selenide has been studied by the use of the 4He and 12C ion backscattering techniques. The samples were thin films grown by molecular beam epitaxy on GaAs (100) epitaxial layers followed by evaporation of platinum and annealing in the temperature range 500–800 °C. The diffusion coefficients were determined by the fitting of a concentration independent solution of the diffusion equation to the experimental depth profiles. The activation energy and the pre-exponential factor of the diffusion process were found to be 1.7 eV and 6.4×10−6 cm2/s, respectively.