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.
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.
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.
Light induced effects on low frequency measurement of small signal driven conductance and transconductance of GaAs MESFET's have been studied. Two versions of a 1 micrometers gate length MESFET fabricated in our laboratory were evaluated; one with ion implanted channel formed in GaAs buffer layer, the other with MOCVD epitaxial doped layer deposited on an undoped GaAs buffer layer. The values of small signal equivalent circuits elements were measured in the linear and saturated regions of I-V characteristics at frequencies from 10 Hz to 150 kHz. Optical excitation during the measurements was provided by red and IR LED's. The epitaxial channel structures showed to have small drain conductance and transconductance frequency dependence. The small signal parameters values were influenced by illumination in the whole measurement frequency range. The implanted channel structures demonstrated, in addition to a large frequency dispersion, a `resonance-like' peak at the transition frequency of 400 Hz to 600 Hz. This phenomenon was related to the dominant deep trap level (Ea equals 0.360 eV) located at the substrate--channel interface, which was found by temperature measurements.
A 1 micrometers gate GaAs MESFET designed for the lower X-band frequencies has been fabricated and characterized. A MOCVD-grown, Se-doped channel layer with 3900 cm2/Vs carrier mobility and a recessed gate structure resulted in a maximum device transconductance of 180 mS/mm. Transistor microwave performance was characterized by the measured gain of 8 dB and noise figure of 3.5 dB at 9.375 GHz. S-parameters measurements in the frequency range 1 divided by 12 GHz allowed for evaluation of small signal equivalent circuit parameters.