Bogusław Boratyński

Technology and characterisation of GaAsN/GaAs heterostructures for photodetector applications

The nitrogen-containing conventional AIIIBV semiconductor alloys, so-called diluted nitrides (AIIIBV-N), have been extensively studied recently. Unusual properties of these materials make them very promising for applications in lasers and very efficient multijunction solar cells. This work presents the technology and properties of undoped GaAs1-xNx/GaAs heterostructures used as active regions in the construction of metal-semiconductor-metal (MSM) photodetectors. The atmospheric pressure metal organic vapour phase epitaxy (APMOVPE) was applied for growing MSM test structures. Their structural and optical properties were examined using high resolution X-ray diffraction (HRXRD), photoluminescence (PL), and photoreflectance spectroscopy (PR). Chemical wet etching was applied for forming an active region and a multifinger Schottky metallization was used as MSM contacts. Dark and illuminated current-voltage characteristics were measured. Based on the obtained results, the main detector parameters as responsivity and spectral response were estimated

Growth of high-quality GaN and AlxGa1-xN layers by an MOVPE technique

AlxGa1-xN layers with 0.02 xGa1-xN layer grown on it were evaluated by high resolution X-ray measurements, their surface morphology was observed with SEM and Nomarski optical microscope. Electrical properties of the layers were determined by C-V measurements performed at 100 kHz and 1 MHz using mercury probes. The aluminum incorporation into the solid phase during the growth process has been studied. As a result high quality AlxGa1-xN/GaN layers for electronic application have been deposited.

Stability of ZnO nanofibers in processing liquid agents

The aim of the research was to determine the impact of developers, removers and solvents on the stability of ZnO nanofibers. Surface imaging of nanofiber morphology was studied using Scanning Electron Microscope. From the obtained results a set of factors which have the least influence on the etching of ZnO nanofibers during device processing was selected. The dependence of the grains size on the fibers robustness in the liquid solutions was investigated. It was found that the nanofibers calcinated at higher temperatures were more stable. This was due to the grain size of the fiber as the fibers calcinated at higher temperatures revealed larger grain size. The studies have shown that smaller grains were dissolved much faster, leaving the porous core of the ZnO nanofiber.

Measurements of high-speed MSM photodetectors

GaAs MSM photodetectors with AlAs/GaAs DBR structures designed for an operating wavelength of 840 nm were characterized in the frequency and time domains. The frequency response of the MSMs, using a lightwave set-up and HP8408 network analyzer, was measured. The photodetector response to the optical pulse of a fast laser diode excitation was evaluated. 3-dB bandwidth in excess of 4 GHz was obtained. Frequency and pulse responses dependence on photodetector bias was characterized.

Growth and characterisation of GaN epitaxial layers

Layers of monocrystalline GaN were grown at different temperatures by atmospheric pressure metalorganic chemical vapour deposition (MOCVD) method on the sapphire substrates. The high quality of the layers was confirmed by X-ray diffraction and photoluminescence spectra measurements. For comparison purposes, simultaneous growth on a-plane and c-plane sapphire substrates was performed for each of the experiments. The GaN layers grown on either a-plane or c-plane sapphire were oriented with the GaN c-plane (0001) parallel to the substrate. The 325 nm line of He-Cd laser was used as an excitation source for photoluminescence experiments. Photoluminescence spectra showed near band peaks and broad yellow band emission at 77 K.

Surface passivation of MSM photodetectors made on GaAsN epitaxial layers

In this paper application of Si3N4, AlN and polyimide to passivate GaAsN/GaAs MSM photodetectors is presented. The MSM structures were made on the undoped GaAsN epitaxial layers in which concentration of nitrogen was varied from 1.0 to 2.6 %. The dark and illuminated I-V characteristics of the devices are presented. Comparison of the dark current value and photoresponse obtained, for selected wavelengths in visible and IR range, from the MSM devices with different passivation layers is provided. Measurements of the dark current and photoresponse in the unpassivated and passivated MSM structures allowed to estimate relation between the bulk and surface components of the dark current. Therefore crystal quality of the epitaxial layers grown in different process conditions could be compared.

Surface potential measurements of a single ZnO nanofiber

In the present study determination of the impact of various gas atmospheres on the surface potential distribution of the electrospun ZnO nanofiber was carried out. Analysis of surface properties was performed using a Scanning Surface Potential Microscopy (SSPM). Obtained results proved homogeneity of the electrical and structural properties along the fiber. The effect of majority carriers depletion in metal oxides in oxidizing gas atmospheres was confirmed by changing the surface potential distribution of the fibers. Measurements performed in dry and humid atmosphere of nitrogen and air could clarify the role of water vapor on the properties of ZnO fibers.

Electrospun ZnO nanofibers for sensors application

In the presented work, a review of electrospun ZnO nanofibers in sensor applications are shown. Devices sensed on harmful substances such as: toxic and combustible gases or volatile organic compounds vapours are included. Various constructions of sensors and methods of their fabrication are compared. Sensing properties of semiconducting metal oxides 1D structures have also been discussed. Technological issues of fabricated devices with electrospun ZnO nanofibers using a standard microelectronic technology especially photolithography and lift-off process was shown. Solutions of the process technology improvement using protective layer will also be presented.

GaN MSM UV photodetectors

GaN Schottky diodes and MSM UV photodetectors were fabricated on GaN/sapphire substrates. Schottky contacts were characterized in a temperature range up to 250/spl deg/C above RT. The MSM photodetector response to 300 nm laser wavelength was measured. Output signal dependence on the detector bias was evaluated. The responsivity of 0.3 A/W was estimated.

Investigation of INGAAs/GAAs photodetectors with ALAs/GAAS nanolayers

The results of investigation of two types of resonant cavity enhanced (RCE) photodetectors PIN and MSM are presented. The structures were designed for wavelength range of870nni I OOOnin; thus the In,GalJs absorption layer with proper composition of indium has been used as am active layer. All structures have been fabricated using Metal Organic Vapour Phase Epitaxy (MO VPE) growth on GaAs substrates with dflerent buffer and matching layer conjguration. For design of the photodeteclor of selective wavelength the resonant cmiily has been fornred with the use oJa Bragg reflector structure consisting oJ 10 pairs of AIAs/GaAs (76/GS.Snn,). The active InGaAs layer was deposited in one process on all substrates with different AIAs/GaAs namolayers conJguration. The device structures were fabricated using a standard W I C processing.