A. Cavus

Red–green–blue photopumped lasing from ZnCdMgSe/ZnCdSe quantum well laser structures grown on InP

Room-temperature optical pumped lasing emission in the red, green, and blue has been obtained from ZnCdMgSe/ZnCdSe quantum well (QW) laser structures grown on InP substrates. The structures are nearly identical, except for variations in the thickness and/or composition of the QW layer. No other single set of semiconductor materials has been demonstrated whose structures are pseudomorphic on one single substrate, and produces light emitters throughout the entire visible range. Our results demonstrate the potential for these materials as integrated full color display devices.

MBE growth of lattice-matched ZnCdMgSe quaternaries and ZnCdMgSe/ZnCdSe quantum wells on InP substrates

We report the growth and characterization of a new wide bandgap II-VI alloy, ZnxCdyMg1-x-ySe, grown lattice-matched to InP. High quality quaternary layers with bandgaps ranging from 2.4 to 3.1 eV were grown by molecular beam epitaxy. The bandgaps and lattice constants were measured using photoluminescence and single crystal Θ-2Θ scans. Quantum well structures with quaternary barriers and ZnCdSe wells were also grown, entirely lattice matched to InP. Their photoluminescence properties suggest that these materials are suitable for the design of visible semiconductor lasers spanning the blue, green, and yellow regions of the visible range. The absence of strain in these heterostructures is expected to improve the reliability of the materials in device applications.

ZnCdSe/ZnCdMgSe quantum wells on InP substrates for visible emitters

We have grown ZnCdSe/ZnCdMgSe quantum well (QW) structures nearly lattice matched to InP substrates. Emission energies from 2.307 to 2.960 eV were measured by low‐temperature photoluminescence at 10 K for samples with QW thicknesses between 5 and 80 A. By using exactly lattice‐matched QWs, the lower limit of the energy range can be lowered to about 2.2 eV (at 10 K). We propose that these structures could be used in entirely lattice‐matched semiconductor lasers operating at room temperature in the blue, green, and yellow regions. Because of the absence of strain, these materials are expected to be less prone to degradation than the current blue‐green lasers grown on GaAs.

Photo-pumped ZnCdSe/ZnCdMgSe blue-green quantum well lasers grown on InP substrates

We report the operation of new photo-pumped blue-green ZnCdSe/ZnCdMgSe graded-index separate confinement heterostructure single quantum well lasers grown lattice matched on InP substrates. Laser emission at 512 nm was observed. The T0 value is 150 K at room temperature. These materials are proposed as alternative materials for the fabrication of visible semiconductor lasers.

MOLECULAR BEAM EPITAXIAL GROWTH OF HIGH QUALITY ZN1-XCDXSE ON INP SUBSTRATES

High quality, lattice matched Zn1−xCdxSe has been grown on InP substrates by molecular beam epitaxy. The quality of the epilayers was monitored by reflection high energy electron diffraction, and by low temperature photoluminescence and transmission electron microscopy (TEM). The use of an As flux during the pregrowth substrate treatment followed by a low initial growth temperature were needed to optimize the growth. TEM images of samples grown under these conditions show abrupt interfaces and good crystalline quality. Epilayers exhibit excellent optical properties, indicated by a very narrow, high intensity near‐band‐edge excitonic emission peak (full width at half maximum of 10 meV), and almost negligible deep level emission.

N-type doping of lattice-matched ZnCdSe and ZnxCdyMg1−x−ySe epilayers on InP using ZnCl2

Chlorine on Se-site forms a shallow donor for ZnSe. In this article, we use Cl, obtained from ZnCl2, as the n-type dopant for ZnxCdyMg1−x−ySe lattice matched to InP, a new wide band gap II-VI material grown by molecular beam epitaxy. An 800 A p-type doped InGaAs buffer layer was grown to improve the doping behavior, consistent with improved crystalline quality. The highest free-carrier concentrations measured by Hall effect are 7×1018 cm−3 with mobility of 240 cm2/V s and 3×1018 cm−3 with mobility of 230 cm2/V s for Zn0.5Cd0.5Se (77 K Eg=2.17 eV) and ZnCdMgSe (77 K Eg=2.74 eV), respectively. A small systematic reduction of maximum carrier concentration was observed as the quaternary layer band gap is increased. No deep level emission is introduced by the chlorine dopant. High n-type doping levels, consistent with semiconductor laser applications were achieved for quaternaries of band gaps as high as 2.9 eV.

Improvement in quality of epitaxial Zn0.5Cd0.5Se layers grown on (001) InP substrates by using an InP buffer layer

Zn1−xCdxSe (x≈0.5), a II–VI wide band gap semiconductor, is grown lattice matched by molecular beam epitaxy on (001) InP substrates. The effect of incorporating an InP buffer layer on structural and optical properties of the ZnCdSe films is studied. Transmission electron microscopy shows that a reduction in the density of stacking faults by two orders of magnitude (from 5×109 down to 5×107/cm2) is realized by use of the buffer layer. Grown-in Shockley-type stacking faults are the only defects observed in the ZnCdSe. The (004) x-ray diffraction rocking curve becomes as narrow as 73 arcsec, and the photoluminescence emission peak becomes narrower and more intense. The lower defect density is attributed to the overall improved InP surface allowing for better two-dimensional nucleation of II–VI growth.

Molecular beam epitaxial growth of lattice-matched ZnxCdyMg1-x-ySe quaternaries on InP substrates

Abstract We report the molecular beam epitaxial (MBE) growth of lattice-matched Zn x Cd y Mg 1− x − y Se quaternaries on InP substrates having a wide range of band gaps. The composition and, thus, band gap and lattice constant, can be accurately controlled by adjusting the group II fluxes. By optimizing the growth condition and incorporating of a III–V buffer layer, we have grown very high-quality quaternary layers. Our best lattice-matched samples exhibit double crystal X-ray rocking curves with full-width-at-half-maximum (FWHM) about 460 arcsec and photoluminescence line widths about 60 meV at 77 K for a band gap of 2.8 eV. These materials can be used for the fabrication of lattice-matched semiconductor lasers that can emit throughout most of the visible range, from yellow to blue.

Optimized growth of lattice-matched ZnCdSe epilayers on InP substrates

Ternaries and quaternaries of ZnCd(Mg)Se can be grown lattice-matched to InP substrates with band gaps spanning most of the visible range, having potential applications as visible light emitters. The quality of these materials is very sensitive to the surface preparation of InP substrates and the initiation of growth. In this paper, we report the details of the growth initiation of ZnCdSe epilayers on InP substrates. The composition of ternary alloy, and thus the lattice-mismatch to InP, was controlled by adjusting the Zn and Cd fluxes. A fast substrate deoxidation, followed by initial low-temperature growth results in two-dimensional growth and substantial improvements of ZnCdSe epilayers. These results along with observations on the use of InGaAs and InP buffer layers indicate that control of the interface chemistry is essential to obtain high-quality materials.

Growth of wide bandgap II-VI alloys on InP substrates by molecular beam epitaxy

We have grown high quality lattice-matched ZnCdSe and ZnSeTe on InP. To optimize the interfaces, the initial growth temperature was lowered and an As flux was used during the thermal treatment of InP substrates prior to epitaxial growth. Under optimized condition, 2D nucleation was observed by reflection high energy electron diffraction (RHEED) throughout the entire growth. Photoluminescence (PL), photoreflectance (PR), transmission electron microscopy (TEM) were used to carry out the sample characterization. Low temperature PL spectra for ZnCdSe show a narrow excitonic emission. PR spectra from ZnCdSe samples also suggest very high quality layers. The ZnSeTe exhibits a strong defect level emission at energy close to band gap and very weak deep level emission. TEM study suggest that the interfaces are comparable to those obtained between ZnSe and GaAs. These results, combined with the new possibilities from these materials, make InP an attractive substrate for II-VI epitaxy.