This paper presents a theoretical analysis for the dark current characteristics of different quantum infrared photodetectors. These quantum photodetectors are quantum dot infrared photodetectors (QDIP), quantum wire infrared photodetectors (QRIP), and quantum well infrared photodetectors (QWIP). Mathematical models describing these devices are introduced. The developed models accounts for the self-consistent potential distribution. These models are taking the effect of donor charges on the spatial distribution of the electric potential in the active region. The developed model is used to investigate the behavior of dark current with different values of performance parameters such as applied voltage, number of quantum wire (QR) layers, QD layers, lateral characteristic size, doping quantum wire density and temperature. It explains strong sensitivity of dark current to the density of QDs/QRs and the doping level of the active region. In order to confirm our models and their validity on the practical applications, a comparison between the results obtained by proposed models and that experimentally published are conducted and full agreement is observed. Several performance parameters are tuned to enhance the performance of these quantum photodetectors through the presented modeling. The resultant performance characteristics and comparison among them are presented in this work. From the obtained results we notice that the total dark current in the QRIPs can be significantly lower than that in the QWIPs. Moreover, main features of the QRIPs such as the large gap between the induced photocurrent and dark current open the way for overcoming the problems of quantum dot infrared photodetectors.

A self-consistent time-domain travelling-wave model for the simulation of self-assembled quantum dot (QD) vertical cavity surface emitting lasers (VCSELs) is developed. The 1-D time-domain travelling-wave model takes into consideration of time-varying QD optical susceptibility, refractive index variation resulting from intersubband free-carrier absorption, homogeneous and inhomogeneous broadening, and QD spontaneous emission noise source. Carrier concentration rate equations are considered simultaneously with the travelling wave model. Effects of temperature on optical susceptibility and carrier density in the active region are taken into account. The model is used to analyze the characteristics of 1.3-µm oxide-confined QD InAs-GaAs VCSEL. The field distribution resulting from time-domain travelling-wave equations, in both the active region and distributed Bragg reflectors, is obtained and used in finding the device characteristics including light-current static characteristics considering the thermal effect. Furthermore, the dynamic characteristics and modulation frequency response are obtained in terms of inhomogeneous broadening.

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Although there are various Medium Access Control (MAC) protocols proposed for Wireless Sensor Network (WSN), there is no protocol accepted as a standard specific to it. This paper deals with completing the design of our previously proposed MAC for WSN by proposing a channel access mechanism (CAM). The CAM is based on developing a backoff mechanism which mainly differentiates nodes’ backoffs depending on their different identification numbers, and it employs a performance tuning parameter for reaching a required performance objective. The probability distribution of the backoff period is constructed and Markov chain modeling is used to analyze and evaluate the CAM against the IEEE802.15.4 slotted CSMA/CA based on single- and multihop communication with respect to the reliability, the average delay, the power consumption, and the throughput. The analysis reveals that the required performance of CAM against the IEEE slotted CSMA/CA can be obtained by choosing the maximum backoff stages number and the tuning parameter value and that CAM performs better than the IEEE with larger nodes number. The multihop scenario results in a good end-to-end performance of CAM with respect to the reliability and delay becomes better with lengthier paths at the expense of increasing the energy consumption.

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This paper aims at designing a Timing Structure Mechanism (TSM) for Wireless Sensor Network (WSN) MAC, with specifying its respective logical topology, especially suitable to the monitoring applications, differentiated and characterized from the existing time bounding strategies, paving for a good performance channel access mechanism. The work proposed in this paper is based on classifying the monitoring applications so as to designing efficient setup and benefiting from the node's capabilities in dividing the network into sub-networks. By evaluating TSM against a cluster-tree IEEE802.15.4 in the two cases of one channel and multi-channel clusters, the simulation results showed that with varying the area, the TSM performs better than the two cases of IEEE802.15.4 in terms of lifetime, end-to-end delay, loss percentage by on average 103.44% and 61.84%, 96.59% and 95.37%, and 88.59% and 87.52%, respectively. Also, in case of increasing the node density, TSM is better in terms of the same parameters by on average 446.58% and 356.05%, 98.04% and 95.62%, and 77.62% and 75.2%, respectively.

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