Iwona Zborowska-Lindert

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

Epitaxial regrowth of InP/InGaAs heterostructure on patterned, nonplanar substrates

Abstract The main goal of the studies on epitaxial regrowth process of InP on patterned substrates is to gain knowledge about growth rates and interface quality on various areas to improve the fabrication technology for future applications. Prepared samples were measured at every step of the process by scanning electron microscope (SEM), optical microscope with dark field and phase contrast modes, atomic force microscope (AFM) and also using optical profilometer WLI (White Light Interferometer). Fabrication steps were divided into three main groups. First was the epitaxial growth of 5 µm thick InP layer. Next was patterning, which was made by applying a mask film on the epilayer. Shapes of the mesas after wet chemical etching with photoresist as a mask as well as the shapes of mesas slopes were irregular on the whole substrate area. These problems were solved by the use of silicon nitride mask. The mesas shapes and their slopes became then regular, independently of etching depth. Second fabrication step was etching of selected area. Couple of solutions were examined, but in details HCl:H3PO4 mixture in various proportions, which gave the best results in mesas shapes and orientations relative to the substrate. After that, the etching mask material was removed from the epilayer using a buffered hydrofluoric acid (BHF). The last step was epitaxial regrowth. To see how the epitaxial growth process was performed on different areas of patterned substrate it was suggested using a “sandwich”, which consisted of 50 layers of indium phosphide and indium gallium arsenide. This idea helped to understand the phenomena occurring during the epitaxial growth on that kind of substrate. The highest growth rate occurred on the top of the mesas and the lowest on their slopes. Described experiments are introduction to the studies on epitaxial growth of buried heterostructure (BH).

Preparation and properties of Zn delta-doped GaAs/AlGaAs heterojunction phototransistor

We have prepared, characterized and discussed the performance of AlGaAs/GaAs heterojunction bipolar phototransistor (HPT) including Zn delta-doped base. Due to the existence of Δ-doped sheets located in the middle of undoped GaAs base the Δ-doped HPT devices exhibit low dark current, nearly zero offset voltage, saturation voltage ~0.4V, and rise and fall times in ns range at wavelength of 850nm up to 6V of applied voltage. Due to avalanche multiplication behavior at the collector junction, an increased optical gain G>10 can be reached for applied voltages in the range of 6-12V. For voltages higher than the device breakdown voltage (~12V) switching and negative differential resistance (NDR) effect is measurable in the inverted mode of operation.

Investigation of the electrical properties of undoped gallium arsenide epitaxial layers

In this investigation we have measured the electron concentration n=7/spl times/10/sup 15/ cm/sup -3/ in the undoped epitaxial GaAs layer grown on the well conducting GaAs substrate, I-V characteristic resistance of the Schottky junction formed in that layer and we have evaluated layer resistivity /spl rho/=0.2 /spl Omega/ cm, barrier potential /spl phi/=0.785 V, ideality factor /spl eta/=1.08 and series resistance R/sub s/=5 /spl Omega/ of the Schottky junction. Then we have measured I-V characteristic between the coplanar ohmic contact formed on the undoped epitaxial GaAs layer grown on SI GaAs substrate and we have evaluated breakdown electric field E/sub T/=1.5 kV/cm, sheet resistivity R/sub s/=10/sup 9/ /spl Omega//0, and layer resistivity /spl rho/=5/spl times/10/sup 4/ /spl Omega/ cm.

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.

Low temperature investigation of electrical and optical properties of InGaAsN/Gas QW Schottky barrier photodetectors

This work presents electrical and optical properties of Schottky barrier photodetectors containing the triple quantum well (MQW) InGaAsN/GaAs structures grown by atmospheric pressure metal organic vapour phase epitaxy. The peaks corresponding to optical transitions in MQW were identified by photocurrent spectroscopy and compared with simulations. The measurements revealed that there are two embedded and overlapped QW which can be simulated as InxGa1-xAs1-yNy/GaAs QW and InxGa1-xAs/GaAs QW with appropriate width and composition. This effect can be assigned to the interdiffusion between QW and GaAs during the structure growth. The low temperature spectral measurements revealed the shift and intensity of optical transitions in particular QWs.

Tunnel junction technology for multijunction solar cell applications

Solar cells are very promising renewable resource. High efficiency of AIIIBV based solar cells are achieved in multijunction constructions. The technology of these devices is very difficult due to the complex electrical and optical interactions between the different semiconductor layers. Usually, the individual subcells are interconnected via Esaki tunnel diodes. This work presents the technology and computer modelling of GaAs based tunnel diodes which will be applied in tandem GaAs/InGaAs solar cells. Designed structures were grown by atmospheric pressure metal organic vapour phase epitaxy. Simulation results as well as dopant profiles and measured DC I-U characteristics of the obtained tunnel diodes are presented and discussed.

Electric power supply sourced from within fiber optic cable

In the paper, authors present an example of a simple and cost effective system of electric power supply by means of optical fiber. In many cases of physical measurements, it is very important to avoid excessive distortion to measured quantity. One of this is measurement of electromagnetic field of radio frequency. This is of concern in both, far- and near field examination. RF field measurement can be performed by direct measurement of the field at a point of interest or by measurement of the field scattered by a dedicated probe. One of the most important properties of this method is its low influence to the field under test. The full advantage of the system can be taken when the probe can be powered and controlled be means of optical fiber.

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.

Fiber- to integrated-optics structure coupling

In presented work, analysis, classification, and selected methods of solving problems connected with coupling optical fibers to integrated optic structures has been shown. The construction and technology of PIN and MSM type detectors and Mach-Zehnder modulator has been described. Several variants of package constructions have been proposed for optical fibers to optoelectronic devices coupling.