Project Founder: TÜBİTAK (1001)

Project Number: 121F169

Project Title : 2D TMDC/MEMS Hybrid Wavelength Tunable LED, (TUBİTAK 1001)

In this project, we aim to fabricate and characterise a p-n junction 2D MoTe2/MEMS based Hybrid Wavelength Tuneable Light Emitting Diode (LED), which consist of a 2D material-based LED with extraordinary optoelectronic properties and a Micro Electromechanical System (MEMS). The budget of the Project is 720 000 TL.

 

Project budget: 719.837 TL

Project Duration: 15/09/2021 - 15/09/2024, 36 months

Project Team: Assoc. Prof. Dr. Fahrettin Sarcan (Project Coordinator), Prof. Dr. Ayşe Erol (Researcher), Dr. Yue Wang (Researcher), Kerem Bostan (Scholarship student), Ceyda Akın (Scholarship student)

Project Founder: TÜBİTAK

Project Number: 120F062

Project Title : InGaAs light-emitting devices based on Gunn Diode

Light emission based on Gunn effect is the band to band recombination of impact ionised non-equilibrium electron-hole pairs in the propagating high field domains along with the Gunn diode; which is biased above negative differential resistance (NDR) threshold. Spontaneous emission from high field domains propagating along a bulk GaAs semiconductor was first reported at the end of the 1960s. Later, first Fabry-Perot and vertical cavity surface emitting Gunn light-emitting devices with an n-type GaAs epilayer as the active layer was fabricated and light emission at 830nm-850nm was detected at 77K. A recent study was on Gunn light-emitting devices based on Al_0.08Ga_0.92As with or without a waveguide structure, and emission at 806nm with a full width at half maximum (FWHM) of 35nm was observed at room temperature The operation wavelength of this device is limited with band edge of GaAs or AlGaAs. In the project, the active layer of the Gunn diodes is constituted from InGaAs semiconductor in order to extend wavelength around 1550nm.  Gunn diode constituted from only one type doped epilayer as the active layer, is different with its operational conditions from a conventional p-n diode laser structure which needs a forward bias for lasing, while Gunn laser is operated under both voltage polarities. We will study both waveguided or non-waveguided Gunn diodes in the project.

 

The basic structure of the device is composed of an n-type InGaAs epilayer grown on InP with having different doping densities. Following the characterisation studies on these structures, ideal devices with the highest emission intensity and lowest FWHM values and stable Gunn oscillations will be determined and are used in the waveguided structures. The waveguided structure to enhance the emission intensity and reduce the FWHM will be designed to have an n-type InGaAs epilayer sandwiched between wideband materials, InAlAs or AlGaAs to well confine the emitted photons in InGaAs active layer. The samples are defined in a simple bar structure with different channel lengths and widths. The fabrication process will be carried out using conventional photolithography techniques. The devices will be fabricated to have channel widths of 2mm -500mm to observe the effect of device geometry on device performance.  Hall bar-shaped structures are also fabricated. High-speed I-V measurements for determining the electric fields forming impact ionisation process, spectral Electroluminescence measurements for determining emission wavelengths, and Electroluminescence vs electric field measurements for finding light emission threshold will be carried out, and Photoluminescence measurements will be carried out to determine bandgap of InGaAs. The experiments will be done temperature-dependent.  The growth of the devices will be carried out at Sivas Cumhuriyet University Nanophotonic Research and Application Centre using MOCVD. The fabrication and characterisation of Gunn diodes will be carried out in İstanbul University Science Faculty Physics Department Nano and Optoelectronics Research Laboratories.

Project budget: 949.837 TL

Project Duration: 01/08/2020 - 01/02/2023, 30 months

Project Team: Ayşe Erol (Leader), Selman Mutlu (Researcher), İlkay Demir (Researcher), İzel Pertikel (scholar), Göksenin Kalyon  (scholar), Saleh Mohammad AMINI (scholar)

 

Outcomes: 2 presentations so far

Project Founder: TÜBİTAK

Project Number: 110T874

Project Title: Influence of bismuth concentration on electronic transport properties in dilute bismide modulation doped GaAsBi/GaAs quantum well structures

 

In the project, effects of Bismuth on optical and electronic transport in n- and p- modulation doped quantum well structures with various bismuth concentration will be investigated. The samples to be used wwas designed by project team and was them grown at Tampere Technical University, Finland. Optical properties was studied using Photoluminescence and Photo-modulated Reflectance techniques, whereas Hall Effect and magnetotransport measurements was be carried out for determining electronic transport mechanisms. Moreover, high speed I-V measurements will be carried out to determine saturation velocities of electron and holes and probe the existence of NDR effect.

 

In the theoretical stage of the project, the electronic band structure of the samples was determined by using finite element methods. Solving self-consistent Schrödinger-Poisson equation, the characteristic physical properties of the system was obtained. Also we obtained the intersubband and interband optical transition energies radiative and nonradiative transition time for the considered structure. The obtained theoretical results will be compared with experimental results.

 

 

Project budget: 505 000 TL

Project Duration: 01/04/2016 - 01/04/2019, 36 months

Project Team: Ömer Dönmez (Leader), Ayşe Erol (researcher), Saffettin Yıldırım (researcher), Ferhat Nutku ((researcher), Mehmet Çetin Arıkan (advisor).

Outcomes: 1 MSc thesis, 5 papers, 4 presentations

Project Founder: TÜBİTAK

Project Number: 113F277

Project Title : Resonant Cavity Enhanced GaInNAs-based  Photodetectors with Gain for Operation at 1.3 μm

In order to meet the increasing demand of large volumes of data traffic at high rates over long distances, information is sent as optical signals (short laser pulses) through optical fibres. Optical fibre networks have two wavelength regions (windows) with small attenuation of the optical signals. The first of these is the one at around λ= 1.55 μm which, with the application of wavelength division multiplication (WDM), is already very heavily utilised in long haul communication systems. The second window is centred around λ= 1.3 μm, it has a slightly higher attenuation and therefore suitable for shorter distance (metro and local) networks. The main components of an optical communication system are lasers, modulators, optical fibres optical amplifiers, photo-detectors and de-modulators. There have been big advances in the development of such components for the 1.55 μm window. However, there is increasing demand for components for the metro and local networks, those operating at 1.3 μm wavelengths. Photodiode sensitivity is one of the key issues in long-haul fiber optic communication systems. Owing to its internal gain which results from impact ionization, the avalanche photodiode (APD) is frequently the detector of choice over p-i-n photodetectors which have no gain, therefore, low sensitivity. The multiplication region of an APD plays a critical role in determining the overall gain and gain-bandwidth product. Both the multiplication noise and the gain-bandwidth product of APDs are determined by the ratio of the electron and hole impact ionization coefficients, which, for the most III-V compounds, approaches unity at high electric field intensities. In the case of only one type of carriers, for example electrons, are involved in the impact ionization process, for the holes, ionization coefficent is zero, leading to noise-free and wide bandwidth photodiode.  APDs for wavelengths beyond 1.1μm use separate layers for light absorption (narrow band gap) and carrier multiplication (wide bandgap). Currently most optical communications systems use mainly the InGaAs/InP APDs. Control of the electric field at the interface between the layers is critical.

 

The current project is concerned with the development of novel photodetectors for the 1.3 μm window, with high sensitivity, fast response, low noise and suitable for the WDM applications, thus with the ability to receive optical information only at a specific wavelength while rejecting others. There are many semiconducting materials that can form the basis of such detectors and each is sensitive to a different wavelength. In this project we are going to use GaInNAs/GaAs structure and both photo absorbing and the internal gain regions are going to be in GaInNAs semiconductor. Dilute nitrides are very different from other semiconductor compounds in that adding small amounts of nitrogen changes its physical properties; lowers its band gap and makes it sensitive to light in the infrared such as 1.3 μm. They can be combined with GaAs technology such as GaAs substrates and GaAs based Bragg reflectors. Furthermore, electrons and holes created by the absorption of light are readily separated in dilute nitride quantum wells, holes are rapidly thermally activated out of the quantum wells as a result of very small valance band discontinuity and then swept away under the influence of the built-in electric field enabling electrons to be accelerated high kinetic energies without recombining with holes. This leads to electron controlled impact ionisation thus, noise-free impact ionisation (avalanche) and high sensitivity to optical intensity. The structure will contain multiple quantum wells (MQW) of GaInNAs/GaAs. MQW structure will be placed between n- and p-type doped layers and this p-i-n photodiode structure will be grown on a wavelength selective cavity, composed of GaAs/GaAlAs DBR layers. The structure will be fabricated in the shape of mesa structure with an aperture at the top. Devices will be grown at semiconductor growth centres at Tampere University of Technology and LAAS. Both are our partners within the EU COST Action MP0805) and have international reputation for the growth of III-V compound semiconductors, particularly very high quality dilute nitride/GaAs quantum well devices including, LEDs, Edge emitting (EELs) and vertical cavity lasers (VCSELs) and semiconductor optical amplifiers (SOAs). Devices will be fabricated at both Essex and once available at the IU fabrication facilities. Material characterization of the samples will be carried out using orthodox techniques such as Hall effect, Photoluminescence (PL), spectral photoconductivity (PC) (All in Istanbul İstanbul University). PL results will be used to determine bandgap of the samples and cavity resonance of the device. Spectral response will be determined with PC. I-V measurements will give information about reverse bias characteristics, breakdown voltage as a function of In and/or N composition and dark current. Speed, bandwidth and noise figure will be determined by transient photoconductivity at Essex University.

 

Project is going to be completed in 3 (three) years. And the stages of the project proposal contain that growth, design and characterization of (a) GaInNAs/GaAs MQW structure, which is both photon absorption and gain region, and (b) resonant cavity, (c) integration of cavity and detector structure, (d) characterization and delivering of the photodetector. At the end of project, it is aimed to develop of a novel photodetector for the 1.3mm with internal gain, fast response, high sensitivity. The project outcome has great potential to be published in respected SCI journals and patented. The main application area of the proposed device will be in optical communications, where there is a need for low cost, high sensitivity high speed photo-detectors operating at near infra-red wavelengths of 1.3 or 1.55 μm. The proposed device has internal amplification, thus high sensitivity; this coupled with low production cost to find applications in both metro and local area networks instead of using low sensitivity Si or InP based pin photodiodes without gain. High sensitivity, high speed photo-detectors impact a wide range of fields from astronomy to environmental protection (for example measurements of atmospheric pollutants and ozone) and defence. Another potential application may be biotechnology in, for example, ultra sensitive fluorescence for single molecule detection or detection of DNA micro arrays. Secure communication systems and quantum cryptography in which detection of single photons is the norm, may be another area of application. There is also a wide range of academic interest in the physical properties of dilute nitrides.

 

Project budget: 444.410 TL

Project Duration: 01/03/2014 - 01/03/2017, 36 months

Project Team: Ayşe Erol (Leader), Mehmet Çetin Araıkan (Researcher), Naci Balkan (Researcher), Fahrettin Sarcan (scholar), Furkan Kuruoğlu  (scholar)

 

Outcomes: 7 papers, 2 PhD thesis, 3 presentations, 1 patent

Project Founder: TÜBİTAK

Project Number: 110T874

Project Title : Investigation of optical properties and electronic transport mechanisms in n ve p- type Modulation Doped Ga_1-xIn_xN_yAs_1-y /GaAs Quantum Well Structures

III-V Semiconductors are indispensable for the realization of today’s optoelectronic devices and this class of materials is also dominant in key high frequency electronics components for wireless communication such as mobile telephone systems. Thank to progresses in epitaxial growth techniques, the miscibility of binary III-Vs and the possibility to stack such layers of various compositions and doping levels (thus creating “heterostructures”) is crucial for all these applications. The tailoring of heterostructure properties is limited by the different lattice constants of the range of available band gaps in order to prevent imperfections. Thus, for example, GaAs-based materials are limited to emission for a maximum of about 1200nm. This limitation can be greatly reduced by incorporating a few percent of nitrogen as a group V element into GaAs or GaInAs, i.e. by creating the so-called dilute nitrides.  Nitrogen into the lattice of host material increases the lattice and causes a reduction in bandgap energy.  Dilute nitride semiconductors are considered as an alternative to current systems for using applications such as laser, photodiode, solar cell, optical amplifier etc. due to their superior performance and low cost production. During the past decade, dilute nitrides, particularly the quaternary material system of GaInNAs/GaAs have attracted a great deal of attention, both because of unusual physical proper- ties and potential applications in a variety of optoelectronic devices. Although the optical properties of GaInNAs/GaAs heterostructures have been extensively studied, there have been comparatively little experimental studies in transport properties in GaInNAs. The introduction of small nitrogen strongly disturbs the conduction band of Ga(In)As leading to significant effect on the electron mobility. A large drop in the electron mobility at room temperature has been observed in GaInNAs alloys, which can be attributed to both the enhanced electron effective mass due to the flattening of the conduction band edge, and the nitrogen complex-related strong alloy scattering. However, the addition of N has negligible effect on valance band, thus the hole mobility is expected to be much higher than that of electron at low temperatures due to the lack of N-related alloy scattering. In the proposed project, it is aimed to investigate optical properties and electronic transport mechanisms in n- and p-type modulation doped GaInNAs/GaAs quantum well structures depending on different nitrogen compositions and post-growth thermal annealing effects.

 

The structures of n- and p-type modulation doped GaInNAs/GaAs quantum wells have been designed by the project leader and growth by Tampere Technical University, Finland where the project leader has collaboration via COST Action MP0805 by using Molecular Beam Epitaxy (MBE). Optical properties will be studied using Photoluminescence, Photoconductivity, Photomodulated Reflectance techniques, whereas Hall Effect and Magnetransport measurements will be carried out for determining electronic transport mechanisms. The temperature dependent mobility of 2D electron gas will be explained using an analytical model that accounts for the most important scattering mechanisms. Under the light of the obtained results, at the last stage of the proposed project, it is aimed to fabricate a laser structure for 1300 nm optical window that will be composed of the most ideal modulation doped structure with high optical quality and highest carrier mobility.

 

In the theoretical stage of the proposed project, the electronic band structure of the samples will be determined by using the k.p method and then the characteristic physical properties of the system will be obtained. Also we will obtain the intersubband and interband optical transition energies, excitonic recombination, impurity binding energies, radiative and nonradiative transition time for the considered structure. The obtained theoretical results will be compared with experimental results.

 

The outcomes of the project prepares a strong background for designing edge and surface emitting laser structures having an active region composed of modulation doped structures.

Project budget: 260.840TL

Project Duration: 01/05/2011 - 01/05/2013, 24 months

Project Team: Ayşe Erol (Leader), Mehmet Çetin Arıkan (Researcher), Hüseyin Sarı (Researcher), Ömer Dönmez (scholar), Fahrettin Sarcan (scholar)

 

Outcomes: 1 PhD thesis, 1 MSc thesis, 7 papers, 3 presentations

Project Title: An Investigation of Electronic Transport in Quantum Well Infrared Photodetector (QWIP) Structures

Project Budget: 345847 TL

Project Funder: Prof. Dr. M. Çetin ARIKAN

Project Number: 108T721

Project Duration (Start and End Dates): April, 2009 - April, 2012

Project Info:

QWIP structures are devices that have wide application areas in the civil and defense industries, have an important place among modern quantum devices and are constantly being developed with new designs. In recent years, epitaxial crystal growth infrastructure has been established in various institutions in our country. Therefore, within the scope of joint projects, it has become possible to produce these structures in our country and even turn them into devices.

Within the scope of this project, QWIP structures were grown in two different locations, Anadolu University Nano-Dimension Laboratories and IQE company in the USA, using the MBE method, which were originally designed by Professor Dr. Yüksel Ergün et al., from Anadolu University. In the project, structures with the same characteristics obtained from these two different locations were examined comparatively. These examinations show the feasibility of QWIP structures in our country from the design to the production stage.

All the research on QWIP structures in the world is mostly based on vertical transport events. Since this project is a basic science project, it is an important and unique feature of the project that the structures are examined in comparison with the material properties under parallel transport, as well as the device properties examined under vertical transport.

Project Scholary Outputs:

Within the scope of the project, 2 master and 2 PhD students were provided with scholarship support from the project and 2 master and 2 PhD thesis studies were completed. In addition, 6 publications, 5 oral and 15 poster presentations from the project were presented to the scientific world.

1.      F. Nutku*, M. Ç. Arıkan, A. Erol, Y. Ergün, and E. M. Kendirlik, “I-V characterization of a staircase quantum well infrared photodetector,” Phys. Status Solidi (C), vol. 8, no. 5, pp. 1633–1636, May 2011. [Link]

2.      F. Nutku, A. Erol*, M. Gunes, L. B. Buklu, Y. Ergun, and M. C. Arikan, “I–V characterization of a quantum well infrared photodetector with stepped and graded barriers,” Superlattices Microstruct., vol. 52, no. 3, pp. 585–593, Sep. 2012. [Link]

3.      O. Donmez, F. Nutku*, A. Erol, C. M. Arikan, and Y. Ergun, “A study of photomodulated reflectance on staircase-like, n-doped GaAs/AlxGa1-xAs quantum well structures,” Nanoscale Res. Lett., vol. 7, no. 1, p. 622, Jan. 2012. [Link] 

4.      F. Nutku*, A. Erol, M. C. Arikan, and Y. Ergun, “Zero-bias offsets in I–V characteristics of the staircase type quantum well infrared photodetectors,” Appl. Surf. Sci., vol. 318, pp. 95–99, Nov. 2014. [Link]