Scientific Exchange Program

Transcription

1 Scientific Exchange Program Electrical characterization of photon detectors based on acoustic charge transport Dr. Paulo Santos, Paul Drude Institute, Berlin,Germany Dr. Pablo Diniz Batista, Brazilian Center Research for Physcis, Rio de Janeiro, Brazil Abstract In this project, we are proposing a scientific exchange program involving investigations on a novel concept for photon detector developed at Paul Drude Institute, Berlin, Germany. This device is based on the transport of electrons and holes photo-excited by the incident photons by a SAW in a semiconductor layer. Detectors based on this principle are expected to achieve single-photon sensitive levels if combined with singleelectron transistors[5]. Sensitive photon detection and emission are of paramount importance for the emerging fields of quantum information processing and quantum communication. The research activities will address the light absorption properties and the acoustic carrier transport in detector structures based on GaAs, InGaAs and Si layers. The electrical characterization of the devices also creates the opportunity to test and study the efficiency of a low-cost semiconductor parameter analyzer developed at Brazilian Center for Physics Research (CBPF) to characterize electronic devices for research purposes.

2 1. Introduction In this project, we propose a scientific exchange providing Brazil's participation in the process of electrical characterization of a photon detector based on acoustic charge transport. The scientific exchange will address basic studies of the detectors as well as the development of instrumentation for the characterization of electronic devices, which is an important aspect in research work on semiconductor materials and devices. In the following, I will briefly describe the main features of the electrical characterization of the detector and the program and chronogram of my research work. 2. Photon detector based on charge acoustic transport Surface acoustic waves (SAWs) are elastic vibrations propagating along the surface of a medium. These waves can be conveniently generated in piezoelectric materials through the inverse piezoelectric effect [1,2]. In semiconductors, the moving piezoelectric field of a SAW can trap and transport charge carriers. This principle can be used for efficient photon detection [3,4]. Figure 1 shows the novel concept for sensitive photon detection based on the transport of photogenerated electrons and holes by a SAW in a semiconductor layer by a light pulse. An acoustic wave produces a periodic piezoelectric potential, which moves with the acoustic speed. Optically generated electrons and holes can be trapped in the negative and positive regions of the SAW potential, respectively, and transported by it to the charge detection region, where they will be collected by a p-in junction and measured by an external circuit. Alternatively, single-electron transistors can be used to provide the high sensitivities required for single-photon

3 detection. Three basic processes control the detector operation: (i) the efficiency of electron-hole photogeneration process; (ii) the acoustic transport of the carriers to the detection area; and (iii) the charge detection efficiency. [Figure 1] Schematic view of the detector. Electrons and holes photogenerated at G are transported by the SAW in the channel in between the metal guides (V gn and V gp ) toward the charge detection areas formed by the p- and n-type contacts. 3. Electrical characterization of the photon detector Detectors of the type in Fig. 1 have been fabricated using AlGaAs layers. These devices operate as efficient detectors for wavelengths shorten than 815 nm. In this project, we will study similar devices as well as devices based on InGaAsP materials, which can be used to detect light in the telecommunication range. To study the detector operation, we are going to measure the electrical current at the p and n contacts as a function of different parameters including (i) the

4 acoustic power, (ii) the voltage applied to the p-i-n junction and (iii) the incident photon energy. Most of these experiments require equipments to record the current vs. voltage characteristics of the device. The electrical characterization of these devices will also provide a great opportunity to test a low-cost semiconductor parameter analyzer, which has been recently developed at the CBPF in Brazil. As shown in Figure 2, the equipment developed contains voltage sources, voltage monitors, and current monitors that can be programmed via a user interface. [Figure 2] Schematic view of the semiconductor parameter analyzer using the microcontroller PIC18F45K20 developed at CBPF. Basically, the module has for channel which can be programmed via USB in order to to apply voltage and monitors current as well. The analog electronic circuit has an analog converter connected to a voltage follower, a voltmeter and ammeter for each voltage source. As the analog-to-digital converter of the microcontroller has only one input, it is necessary that all voltages are multiplexed through a programmable gain amplifier. From this diagram, we can

5 infer that the microcontroller can be considered as the core unit, which controls all other peripherals. The tasks performed by the microcontroller are executed in accordance with commands received via USB. The relevance of this low cost equipment is mainly due to the resolution of 1 mv of the voltage sources and the ability to measure currents down to 1 na. Therefore, the module can be used to highlight principles of measurement, instrumentation, fundamental principles of electronics, device testing and characterization in waver or discrete device level. The fundamental nature of these measurements makes them useful in a wide range of applications and disciplines. They can be used in the research labs of universities and semiconductor manufacturers to evaluate new materials, processes, devices, and circuits. Other devices that can be characterized with this instrument include diodes, FET and MOSFET transistors, BJT transistors, photodiodes, and phototransistors, amongst other devices. In order to address the properties of the parameter analyzer in Fig. 2, its characteristics will be compared to the ones obtained with conventional electrometers and commercial semiconductor parameter analyzers. 4. Working program and schedule The research project is planned for 2 months and will be conducted in accordance with the following activities schedule. Weeks 1-2 Weeks 3-4 Weeks 5-7 Weeks 8-10 Setup of measurement system using Measurements on (Al,Ga)As and Si photon detectors Measurements on InGaAsP photon detectors Analysis of the results and preparation of the report of activities

6 5. About the CBPF and Paul Drude Institute Established in 1949 as a partnership by a group of eminent Brazilian physicists (including César Lattes, José Leite Lopes and Jayme Tiomno), the CBPF has played a fundamental role in the education of the first generations of Brazilian and Latin-American physicists as well as in the consolidation of scientific research in experimental and theoretical Physics in Brazil. In 1975, the CBPF was incorporated by the National Council for Scientific and Technological Development (CNPq) and subsequently (in 2000) transferred to the Ministry of Science and Technology (MCT). The institution mission involves (i) basic research in Physics, (ii) the development of applications and (iii) education, training, and improvement of scientific personnel. The CBPF s Postgraduate Program was the first in Physics in Brazil, and has already surpassed the mark of 740 titles including masters (375) and PhDs (371) graduated from the institution. In 2000, it created the first masters degree in Scientific Instrumentation applied to Physics. The Paul Drude Institute is a research institute devoted to materials research on low-dimensional structures based on III-V semiconductors. The Institute has an extensive infra-structure for the growth and processing of semiconductors (clean room, optical lithography facilities, etc). There are alse facilities for probing the electrical and optical characteristics of electro-optic SAW devices including radiofrequency equipment (probe stations, RF and optical network analyser, RF generators, etc); equipment for the detection of SAW fields using optical and scanning probing techniques; and optical spectroscopy facilities including lasers, spectrometers and detectors for a wide energy range.

7 6. Conclusions This project addresses studies of a novel concept for single-photon detector developed at the Paul Drude Institute, Berlin. The studies will initiate a scientific collaboration between research institutions and these experiments to be carried out open the way for testing the low-cost semiconductor parameter analyzer developed in Brazil. 7. References [01] Bill Drafts, IEEE Transactions on Microwave Theory and Techniques 49, 4 (2001) [02] Mauricio M de Lima Jr, Paulo v Santos, Reports on Progress in Physics, (2005) [03] P. D. Batista, M. Gustafsson, M. M. de Lima, Jr., M. Beck, V. I. Talyanskii, R. Hey, P. V. Santos, M. P. Delsing, and J. Rarity, in Proc. SPIE 6583 (PUBLISHER, ADDRESS, 2007), p [04] P. D. Batista, R. Hey, and P. V. Santos, Appl. Phys. Lett. 93, (2008). [05] Talyanskii, V. I.; Milburn, G. J.; Stotz, J. A. H. & Santos, P. V. Acoustoelectric single-photon detector Semicond. Sci. Technol., 2007, 22,