Excess noise measurement in In0.53Ga0.47As

The excess noise due to impact ionization has been measured explicitly for the first time in In/sub 0.53/Ga/sub 0.47/As. By using a phase sensitive detection technique, the noise due to avalanche current was determined even in the presence of high tunneling currents. The excess noise due to pure electron injection measured on a series of thick In/sub 0.53/Ga/sub 0.47/As p/sup +/-i-n/sup +/ diodes suggests large electron to hole ionization coefficient ratio between 3.7 at electric field of 310 kV/spl middot/cm/sup -1/ to 5.3 at 260 kV/spl middot/cm/sup -1/. Excess noise was also measured at fields as low as 155 kV/spl middot/cm/sup -1/ suggesting that significant impact ionization occurs at these low fields. The multiplication and excess noise calculated using published ionization coefficients and ignoring dead space effects, gave good agreement with the experimental data for mixed and pure electron injection

Fast non-recursive extraction of individual harmonics using artificial neural networks

A collaborative work between Northumbria University and University of Peradeniya (Sri Lanka). It presents a novel technique based on Artificial Neural Networks for fast extraction of individual harmonic components. The technique was tested on a real-time hardware platform and results obtained showed that it is significantly faster and less computationally complex than other techniques. The paper complements other publications by the author (see paper 1) on the important area of “Power Quality” of electric power networks. It involves the application of advanced techniques in artificial intelligence to solve power systems problems

Effect of impact ionization in the InGaAs absorber on excess noise of avalanche photodiodes

The effects of impact ionization in the InGaAs absorption layer on the multiplication, excess noise and breakdown voltage are modeled for avalanche photodiodes (APDs), both with InP and with InAlAs multiplication regions. The calculations allow for dead space effects and for the low field electron ionization observed in InGaAs. The results confirm that impact ionization in the InGaAs absorption layer increases the excess noise in InP APDs and that the effect imposes tight constraints on the doping of the charge control layer if avalanche noise is to be minimized. However, the excess noise of InAlAs APDs is predicted to be reduced by impact ionization in the InGaAs layer. Furthermore the breakdown voltage of InAlAs APDs is less sensitive to ionization in the InGaAs layer and these results increase tolerance to doping variations in the field control layer

Field dependence of impact ionization coefficients in In0.53Ga0.47As

Electron and hole ionization coefficients in In/sub 0.53/Ga/sub 0.47/As are deduced from mixed carrier avalanche photomultiplication measurements on a series of p-i-n diode layers, eliminating other effects that can lead to an increase in photocurrent with reverse bias. Low field ionization is observed for electrons but not for holes, resulting in a larger ratio of ionization coefficients, even at moderately high electric fields than previously reported. The measured ionization coefficients are marginally lower than those of GaAs for fields above 250 kVcm/sup -1/, supporting reports of slightly higher avalanche breakdown voltages in In/sub 0.53/Ga/sub 0.47/As than in GaAs p-i-n diodes

Temperature dependence of breakdown and avalanche multiplication in In0.53Ga0.47As diodes and heterojunction bipolar transistors

The avalanche multiplication and impact ionization coefficients in In/sub 0.53/Ga/sub 0.47/As p-i-n and n-i-p diodes over a range of temperature from 20-400 K were measured and shown to have negative temperature dependence. This is contrary to the positive temperature dependence of the breakdown voltage measured on InP/In/sub 0.53/Ga/sub 0.47/As heterojunction bipolar transistors (HBTs) in this and previous works. It is shown that the collector-base dark current and current gain can be the overriding influence on the temperature dependence of breakdown in InP/In/sub 0.53/Ga/sub 0.47/As HBTs and could explain previous anomalous interpretations from the latter

Burst-by-Burst Adaptive Decision Feedback Equalized TCM, TTCM, BICM and BICM-ID

Decision Feedback Equalizer (DFE) aided wideband Burst-by-Burst (BbB) Adaptive Trellis Coded Modulation (TCM), Turbo Trellis Coded Modulation (TTCM), Bit-Interleaved Coded Modulation (BICM) and BICM with Iterative Decoding (BICM-ID) are proposed and characterised in performance terms over the COST 207 Typical Urban (TU) wideband fading channel. These schemes are evaluated using a practical modem mode switching regime. System I represents schemes without channel interleaving, while System II invokes channel interleaving over four transmission bursts. A substantially improved Bit Per Symbol (BPS) and Bit Error Rate (BER) performance was achieved by System II in comparison to System I. BbB-adaptive TTCM was found to give the best performance, when aiming for a target BER of below 0.01%

An InGaAs/AlAsSb Avalanche Photodiode With a Small Temperature Coefficient of Breakdown

Dark current and avalanche gain M on AlAs0.56Sb0.44 (hereafter referred to as AlAsSb) separate absorption multiplication (SAM) avalanche photodiodes (APDs) were measured at temperatures ranging from 77 K to 300 K. To avoid possible ambiguity in breakdown voltage due to edge breakdown and tunneling current, a phase-sensitive detection method with a tightly focused light spot in the center of the device was employed to measure M accurately. An extrapolation of 1/M to zero was used to deduce the breakdown voltage, from which the temperature coefficient of breakdown voltage Cbd was derived. The value of Cbd 1/4 8 mV/K, obtained for AlAsSb SAM APDs, is much smaller than that for commercial Si and InGaAs/InP APDs, as well as other SAM APDs in the literature, demonstrating the potential of AlAsSb avalanche regions in improving the thermal stability of APDs

Impact of secondary education reform on tertiary students’ generic competencies: A case study of associate degree freshmen in Hong Kong

This paper examines the correlation between curriculum reforms and the development of generic competencies among Hong Kong tertiary students (or secondary leavers who were admitted to Associate Degree and Higher Diploma). A total number of 3626 freshmen completed a set of self-assessment questionnaires, which were used to analyse the correlation between five generic competencies, across three academic years from 2010 to 2012. Five of the generic competencies, which were highlighted in the proposed new three-year New Senior Secondary (NSS) academic structure, were measured and compared between students from different academic backgrounds. The finding of the study indicated significantly higher scores in generic competencies for the traditional Hong Kong Advanced Level Examination (HKALE) secondary school curriculum in 2012 compared to earlier cohorts, whilst in general no significant difference was found between students from the traditional curriculum and the new academic structure of the Hong Kong Diploma of Secondary Education (HKDSE) in the mixed ‘double cohort’ year of 2012. The result points to the potential early impact of NSS on students’ generic skill development across both the old and new curriculum

A theoretical comparison of the breakdown behavior of In0.52Al0.48As and InP near-infrared single-photon avalanche photodiodes

We study the breakdown characteristics and timing statistics of InP and In0.52Al0.48As single-photon avalanche photodiodes (SPADs) with avalanche widths ranging from 0.2 to 1.0 mu m at room temperature using a random ionization path-length model. Our results show that, for a given avalanche width, the breakdown probability of In0.52Al0.48As SPADs increases faster with overbias than InP SPADs. When we compared their timing statistics, we observed that, for a given breakdown probability, InP requires a shorter time to reach breakdown and exhibits a smaller timing jitter than In0.52Al0.48As. However, due to the lower dark count probability and faster rise in breakdown probability with overbias, In0.52Al0.48As SPADs with avalanche widths <= 0.5 mu m are more suitable for single-photon detection at telecommunication wavelengths than InP SPADs. Moreover, we predict that, in InP SPADs with avalanche widths <= 0.3 mu m and In0.52Al0.48As SPADs with avalanche widths <= 0.2 mu m, the dark count probability is higher than the photon count probability for all applied biases

GaAs/Al 0.8 Ga 0.2 As avalanche photodiodes for soft X-ray spectroscopy

The soft X-ray spectroscopic performance of a GaAs/Al 0.8 Ga 0.2 As Separate Absorption and Multiplication (SAM) APD was assessed at room temperature using a 55 Fe source. An energy resolution of 1.08 keV (FWHM) was achieved for the 5.9 keV X-rays, at an avalanche gain of 3.5. The avalanche gain also improved the minimum detectable energy from 4.8 keV at unity gain to about 1.5 keV at a gain of 5. Through avalanche statistics analyses, we confirmed that (i) the APD’s FWHM was degraded by X-ray photon absorption within the avalanche region, and (ii) photon absorption in/near the n-cladding layer contributed to an undesirable secondary peak in the spectrum