We discuss low-pressure HVPE growth of ZnSe on GaAs substrates (~350 µm thick) and on OP-GaAs templates (~115 µm thick) that achieved single-crystalline quality ZnSe layers which will be used to develop OP-ZnSe QPM structures for nonlinear frequency conversion devices. Material characterization techniques including SEM, HR-XRD, XTEM, and PL have been used to verify that the ZnSe grown by HVPE has a superior quality to the commercially available ZnSe substrates. Current focus is to obtain thicknesses beyond 500 µm using plain and OP templates for frequency conversion in the MLWIR.
KEYWORDS: Metals, Process control, Chemistry, Dielectrics, Semiconductors, Deep ultraviolet, Vapor phase epitaxy, Sapphire, Transition metals, Control systems
In the expanding field of 2D, hBN serves as the 2D insulator finding application as a non-interacting substrate, passivation layer, and gate dielectric for use with 2D semiconductors, as well as, for deep UV emitters and single-photon sources. This has driven research into synthesis methods for controlled growth form mono to many layer thick films. Here we present on growth of mono to few layer hBN by metal organic vapor phase epitaxy on various substrates from sapphire to transition metals. Models describing growth chemistry for these various substrates are described. The effects growth conditions on properties will also be discussed.
Frequency conversion in orientation-patterned (OP) materials is a leading approach for generating mid- and long-wave IR radiation. Although several phase-matching and quasi-phase-matching (QPM) materials have been investigated to date none of these have met all requirements for power, tunability and frequency range of the pursuit applications. We present an original approach that successfully combines in a QPM heterostructure two of the most promising materials, GaP—a material with lower two and three-photon absorption than GaAs, and GaAs—a material with a mature process for fabrication of high quality OP templates. Up to 300 µm thick OPGaP with excellent domain fidelity has been repeatedly grown with 100 µm/h by hydride vapor phase epitaxy on the robust and high quality OPGaAs templates. Some simplifications of both template fabrication and growth process are also reported. The samples, characterized by AFM, SEM, XRD, EDS and TEM, showed smooth surface morphology and high crystalline quality. Special attention was paid to the interface and especially to the mechanism of forming an intermediate ternary transition layer. This led to determining certain criteria that indicate, which other heteroepitaxial cases would be also successful. Thick growths of GaAsP and GaP on other alternative substrate materials by combining a-close-to-equilibrium with a-far-from-equilibrium processes were also performed. Efforts to develop heterostructures in horizontal and vertical direction have been also made. The success with one less favorable (in point of view of lattice mismatch) case, presented here, indicates that we should have even better results in other cases with closer lattice matches.
Thick hydride vapor phase epitaxially grown orientation-patterned gallium phosphide (OPGaP) is a leading material for quasi-phase matching (QPM) frequency conversion in the mid- and longwave infrared (IR). This is due to its negligible two-photon absorption (2PA) in the convenient pumping range 1 – 1.7 μm, compared with the 2PA of some traditional QPM materials, such as GaAs. In this paper, we describe homo- and heteroepitaxial growth techniques aimed to produce hundreds of microns thick OPGaP on: 1) OPGaAs templates fabricated using an improved wafer-fusion process; 2) OPGaAs templates fabricated by using a molecular beam epitaxy (MBE) for sublattice polarity inversion, but one with and one without MBE regrowth after the inversion. Some of the advantages of the heteroepitaxial growth of OPGaP on OPGaAs templates include: 1) achieving good domain fidelity as a result of the significantly higher OPGaAs template quality; 2) eliminating the needs of using the poor quality commercially available GaP in the production of thick OPGaP material, and 3) suppression of the additional absorption band between 2 – 4 μm (which is due to incorporation of n-type impurities) and, in general, improvement of the IR transmittance in the entire IR region. Combining the advantages of the two most promising nonlinear materials, GaAs and GaP, will accelerate the development of high power, broadly tunable laser sources in the IR which, in addition, will be offered with higher device quality and at a reasonably lower unit cost.
Frequency conversion in orientation-patterned quasi-phase matched materials is a leading approach for generating tunable mid- and long-wave coherent IR radiation for a wide variety of applications. A number of nonlinear optical materials are currently under intensive investigation. Due to their unique properties, chiefly wide IR transparency and high nonlinear susceptibility, GaAs and GaP are among the most promising. Compared to GaAs, GaP has the advantage of having higher thermal conductivity and significantly lower 2PA in the convenient pumping range of 1– 1.7 μm. HVPE growth of OPGaP, however, has encountered certain challenges: low quality and high price of commercially available GaP wafers; and strong parasitic nucleation during HVPE growth that reduces growth rate and aggravates layer quality, often leading to pattern overgrowth. Lessons learned from growing OPGaAs were not entirely helpful, leaving us to alternative solutions for both homoepitaxial growth and template preparation. We report repeatable one-step HVPE growth of up to 400 μm thick OPGaP with excellent domain fidelity deposited for first time on OPGaAs templates. The templates were prepared by wafer fusion bonding or MBE assisted polarity inversion technique. A close to equilibrium growth at such a large lattice mismatch (-3.6%) is itself noteworthy, especially when previously reported attempts (growth of OPZnSe on OPGaAs templates) at much smaller mismatch (+0.3%) have produced limited results. Combining the advantages of the two most promising materials, GaAs and GaP, is a solution that will accelerate the development of high power, tunable laser sources for the mid- and long-wave IR, and THz region.
A series of nonlinear materials including GaAs, GaP, and ZnSe have been examined to determine their suitability for non-linear frequency conversion devices (FCD) and more specifically their use as high power, compact and broadly tunable IR and THz sources for defense and security applications. The more mature GaAs was investigated to reveal the causes for the optical losses that restrict achievement of higher conversion efficiency in quasi-phasematched FCD, while the efforts with GaP were oriented in developing simple, cost effective techniques for fabrication of orientation patterned (OP) templates and optimizing the subsequent thick HVPE growth on these templates. Thus, average growth rates of 50- 70 μm/h were achieved in up to 8-hour long experiments. High optical layer quality was achieved by suitable control of the process parameters. The optimal orientation of the pattern was determined and used as essential feedback aiming to improve the template preparation. This led to the production of the first 300-400 μm thick device quality OPGaP. Efforts to suppress the parasitic nucleation during growths with longer duration or to achieve thicker layers by a 2 step growth process were also made. The main challenge with the newer candidate, OPZnSe, was to establish suitable regimes for hydrothermal growth on plain (001) ZnSe seeds grown by chemical vapor deposition. Two different temperature ranges, 330-350 °C and 290-330 °C, were investigated. The mineralized concentration was also manipulated to accelerate the growth in (111) direction and, thus, to improve the growth in (001) direction. The next material in the line is GaN. The traditional HVPE approach will be combined with a growth at low reactor pressure. Growths will be performed in the next sequence: growth on thin GaN layers grown by MOCVD on sapphire wafers, growth on half-patterned GaN templates with different orientations and, finally, growth on OPGaN templates.
Bulk ZnO crystals were grown by the hydrothermal technique with Al2O3 added to the solution in an attempt to obtain Al-doped ZnO crystals. Aluminum and indium co-doped ZnO were also grown by the same technique. Adding Al2O3 to the growth solution has a significant impact on the ZnO growth ⎯ either preventing overgrowth and dissolving the seed growth or degrading the crystalline quality; nevertheless, the resulting crystals of both Al:ZnO and Al/In:ZnO are highly conductive, similar to In and Ga doped ZnO crystals, with a resistivity approaching 0.01 Ω cm, as revealed by temperature-dependent Hall-effect measurements. Photoluminescence spectra at 18 K show Al0-bound-exciton peak energies of 3.3604 eV on the Zn face and 3.3609 eV on the O face for the Al-doped ZnO crystals. Similarly both an Al0- bound-exciton peak at 3.3604 eV and an In0-bound-exciton peak at 3.3575 eV were found on the Al/In-co-doped crystals. The electrical properties of all group III doped ZnO crystals grown hydrothermally are compared with each other and with Al:ZnO obtained by other growth methods.
Orientation-patterned GaP is a promising nonlinear material for frequency conversion in the mid and longwave IR (2-5
μm and 8-12 μm) by quasi-phase matching. As an alternative to OPGaAs, OPGaP has the advantage of having lower
two-photon absorption in the convenient pumping range 1 – 1.7 μm. We report recent results on development of thick QPM GaP for high power tunable laser sources radiating in the mid IR. Two are the major challenges to producing OPGaP: development of simple techniques for preparation of patterned templates and a technology for fast epitaxial growth of thick, high quality GaP on these templates. The focus was to adapt/simplify the wafer fusion process for OPGaP template preparation. Then increase the growth rate and layer thickness of regrown material, while maintaining vertical domain propagation. The growth experiments were conducted in a horizontal quartz reactor, using a standard hydride vapor phase epitaxial process. The growth was performed on: (i) plain (100) GaP; (ii) half-patterned (HP) and (iii) orientation-patterned (OP) templates, fabricated on (100) GaP. Up to 370 μm thick layers with high crystal and optical quality were reproducibly grown on plain material. Growth on HP templates resulted in up to 470 μm thick layers with rectangular mesa‟s shape. These results were used to determine the optimal substrate and pattern orientations. HVPE growth on OP templates achieved stable growth rates of 50-70 μm/h with domain walls propagating vertically, following the periodicity of the initial pattern, and resulted in the first 350 μm thick device quality OPGaP.
This work investigates properties of surface plasmons on doped metal oxides in the 2-20 μm wavelength regime. By
varying the stoichiometry in pulse laser deposited Ga and Al doped ZnO, the plasmonic properties can be controlled via a fluctuating free carrier concentration. This deterministic approach may enable one to develop the most appropriate stoichometry of ZnAlO and ZnGaO in regards to specific plasmonic applications for particular IR wavelengths. Presented are theoretical and experimental investigations pertaining to ZnAlO and ZnGaO as surface plasmon host materials. Samples are fabricated via pulsed laser deposition and characterized by infrared ellipsometry and Hall-effect measurements. Complex permittivity spectra are presented, as well as plasmon properties such as the field propagation lengths and penetration depths, in the infrared range of interest. Drude considerations are utilized to determine how the optical properties may change with doping. Finite element simulations verify these plasmonic properties. These materials not only offer potential use as IR plasmon hosts for sensor applications, but also offer new integrated device possibilities due to stoichiometric control of electrical and optical properties.
Bulk ZnO crystals were grown by the hydrothermal technique with Ga2O3 or GaN added to the solution in an
attempt to dope with Ga, or co-dope with Ga and N, respectively. Adding Ga2O3 alone to the growth solution
significantly reduces the ZnO growth rate; however, the resulting crystal is highly conductive, with a resistivity
approaching 0.01 Ω cm. In contrast, the addition of GaN had less effect on the growth of ZnO, but the crystal was of
poor quality with a higher resistivity, about 0.1 Ω cm. Photoluminescence spectra at 4 K show Ga0-bound-exciton peak
energies of 3.3604 and 3.3609 eV for the Ga- and Ga/N-doped crystals, respectively; these energies differ slightly from
the literature value of 3.3598 eV, evidently due to compressive strain. Other peaks at 3.307, 3.290, 3.236, and 3.20 eV
were found in the Ga/N-codoped ZnO after the crystal was annealed at 600°C in air. The 3.307 eV peak is the so-called
A line, and likely arises from recombination of a free electron with a neutral N-related acceptor.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.