Solid-state Photodiodes Research Articles

Saturation effects in solid-state photodiodes and impact on EUVL pulse energy measurements

With the advent of extreme ultraviolet lithography (EUVL) it is becoming increasingly important to understand the response of solid-state photodiodes to pulsed radiation where the peak power incident on the device may be quite high even when the average power is modest. The high peak power causes the photodiode signal to saturate and can create errors in the measurement of pulse energy unless the saturation effect is corrected. We have used 532 nm radiation from a frequency-doubled, Q-switched Nd : YAG laser as a proxy for the 13.5 nm radiation used in EUVL and have studied the saturation behaviour of Si photodiodes at peak power densities from less than 0.1 W mm−2 to over 2 × 106 W mm−2. Here we test a previously reported model of saturation at pulse lengths from 8 ns to 1 µs and examine the effect of power density (illumination area) on the saturation behaviour. The saturation parameters measured at 532 nm are used as inputs to the model, and the calibration of a filter radiometer in pulsed 13.5 nm radiation is corrected for saturation effects. The corrected result agrees with the value expected from individual component calibrations, but the uncorrected data differ by more than the combined uncertainty. This result supports the hypothesis that 532 nm radiation is a valid proxy for 13.5 nm radiation when studying saturation behaviour. Finally, we derive quantitative limits imposed by the saturation effects on the use of Si photodiodes in EUVL applications.

Damage to solid-state photodiodes by vacuum ultraviolet radiation

We report experimental results on the stability of photodiodes obtained at three different wavelengths in the vacuum ultraviolet spectral region. Two of these experiments were based on radiation damage inflicted with excimer lasers at 193 and 157 nm and one of them used 135 nm synchrotron radiation. It was found that the detector degradation rate increased considerably with the photon energy and depended on the structure of the photodiodes. Detectors based on the Si/SiO 2 interface were damaged much faster than Schottky-type diodes or Si diodes with metal passivating layers. Possible damage mechanisms to the Si/SiO 2 interface and its electronic structure are reviewed. In the end, a model to quantify the dependence of the damage on the photon energy is introduced.

High-precision stopped-flow mixer for kinetic determinations

Abstract A highly automated, chemically inert, stopped-flow mixing system for rapid kinetic determinations is described. The reactant solutions are drawn into the drive syringes through novel double check valves, which are an integral part of the syringe block. The prime movers for the flow systems are pneumatic cylinders driven by compressed air; air flow is controlled by electromechanical valves actuated by optically isolated zero-crossing switches. The dead time of the flow system is 2–3 ms, depending on the drive pressure. The spectrophotometric detection system consists fo a high-intensity light source, a wavelength selector and a reference detector that are mechanically isolated from the flow system by a quartz fiber-optic light guide. The transducers are solid-state photodiodes. The sample photodiode is mounted adjacent to the output window of the cell to minimize light losses. The signal-to-noise ratio of the photometric system is from 2×102 to greater than 4×4, depending on wavelength, absorbance level, and amount of signal averaging. The reduction of Fe(CN)63− by ascorbic acid was used as a test reaction. Accuracy and precision better than 0.3% were obtained for routine determination. A detection limit of 4.10×10−7 M Fe(CN)63−, or 134 μg kg−1 K3Fe(CN)6, was found for this system.

Effect of optical radiation in a photo-DOVATT

Avalanche photodetectors are very important solid-state detectors currently used in long-distance and wide-band optical communication systems, due to their faster speed of response compared to other solid-state photodiodes. Furthermore, it has been found that by using heterostructures one can improve both multiplication gain and quantum efficiency of such a device. DOVATT is a heterojunction impatt device in which there is one avalanche zone followed by two drift zones at different scattering limited velocities. The device is very useful for generation of high power in the X-band. The present paper examines the effect of optical radiation on such a device. Studies have been made on the frequency-response characteristics of the device. The results show that the device has the potentiality of becoming a powerful photodetector in optical communication systems.

Tests of cesium iodide crystals for an electromagnetic calorimeter

A new electromagnetic shower detector will be constructed for the CLEO II experiment at CESR. It will consist of 8000 CsI(Tl) crystals coupled to solid state photodiodes. Extensive tests on the response of 175 CsI crystals are reported here. Each block measured 5 cm by 5 cm in cross section and 30 cm (16.2 radiation lengths) in depth. A fast and reliable method to determine acceptable light output and uniformity of crystals using a 137Cs radioactive source and photomultiplier readout was successfully developed. For test beam studies each crystal was equipped with four silicon photodiodes connected to a low-noise charge amplifier. Calibration with a positron test beam yielded average light output of 2500 photoelectrons per MeV and showed good correlation with the radioactive source exposures. In the beam tests at 180 (5000) MeV, energy resolutions of 4% (1.5%) and position resolutions transverse to the beam of 1.2 (0.3) cm were achieved. The effects of material between and in front of crystals, non-normal incidence, and staggering of adjacent crystals were studied, and together were found to degrade the energy resolution by only a modest amount. Operation of the system near room temperature will ensure low noise and stable response. The radiation sensitivity of a number of CsI blocks was measured and found to be acceptable for the radiation levels anticipated in CLEO II.

Multiwavelength optical pyrometer for shock compression experiments

A system for measurement of the spectral radiance of materials shocked to high pressures ( approximately 100 GPa) by impact using a light gas gun is described. Thermal radiation from the sample is sampled at six wavelength bands in the visible spectrum, and each signal is separately detected by solid-state photodiodes, and recorded with a time resolution of approximately 10 ns. Interpretation of the records in terms of temperature of transparent sample materials is discussed. Results of a series of exploratory experiments with metals are also given. Shock temperatures in the range 4000-8000 K have been reliably measured. Spectral radiance and temperatures have been determined with uncertainties of 2%.

Sensitive high speed photodetectors for the demodulation of visible and near infrared light

Photomultipliers, solid state photodiodes and avalanche photodiodes are the preferred detectors for the demodulation of light intensity variations at visible and near infrared wavelengths. The principles of operation of these detectors will be described together with their basic construction and operational characteristics. Photomultipliers with the recently developed high efficiency photocathodes for visible and near infrared wavelengths and the high gain dynode arrangements with fast speed of response will be mentioned. The various types of silicon and germanium photodiodes with and without internal current gain will be discussed. Tradeoffs involved in the optimization of quantum efficiency, speed of response, internal current gain and sensitivity to weak light signals will be treated in detail for silicon photodiodes operating at wavelengths either in the visible or at the GaAs (≈0.7–0.9 μm) or YAG (1.06 μm) infrared laser emission lines. The capabilities of germanium avalanche photodiodes for the detection of infrared light at wavelengths up to about 1.6 μm will be mentioned.

Fast Light-Pulse Measurement Schemes

An ultrafast circuit for photodiodes makes it possible to realize the highest fidelity and fastest time domain response capabilities (on the order of 100 ps rise-time response) for measuring fast light pulses. The circuit utilizes triaxial cable as a simple improved means of overcoming the inherent response limitations posed by customary photodiode circuits and components. The triaxial cable circuit can be utilized for both solid-state and vacuum photodiodes, and can be readily adapted to various light-pulse measurement schemes. This paper includes a description of the basic triaxial cable circuit, a calculation of its response capability with a typical photodiode, and an adaptation to a scheme for measuring interpulse intervals of several sequential light-pulse sources.

Coherent light detection in solid-state photodiodes

The operation of solid-state photodiodes as mixers of coherent light is discussed. Particular attention is given to the parameters that influence 1) frequency response, 2) quantum efficiency and 3) sensitivity. The highest mixed frequency that can be detected is determined by carrier transport considerations as well as RC circuit parameters. Output mixed frequencies to 100 kMc can be obtained in appropriately designed structures. Experimental results verifying the existence of photomixing in Si, Ge, GaAs and InAs photodiodes are presented.