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A thin-film solar cell based on a Cu 2 ZnSnS 4 (CZTS) absorber layer deposited by pulsed laser deposition has been fabricated with an Al:ZnO (n-type) window layer and a CdS buffer layer. Some peaks attributed to ( 112), ( 200), ( 220), and (312) planes of CZTS appeared in an X-ray diffraction pattern of a thin film. The composition of the film was Sn-rich and the band gap energy was approximately 1.5 eV. A CZTS film annealed at 500 C in an atmosphere of N 2 had optical characteristics suitable for use in an absorber layer of a thin-film solar cell and was used for a solar cell. The CZTS thin-film solar cell with an active area of 0.092 cm 2 showed an open-circuit voltage of 546 mV, a short-circuit current of 6.78 mA/cm 2 , a fill factor of 0.48, and a conversion efficiency of 1.74%.

PACS 71.55.Ht, 78.55.Hx Photoluminescence from Cu 2 ZnSnS 4 bulk single crystals was studied as a function of temperature and excitation power density. The bulk single crystals showed a broad luminescence between 1.1 and 1.45 eV. The peak energy of the photoluminescence was shifted to higher energy side when the excitation power density was increased. The origon of the photoluminescence was attributed to donor -acceptor pair recombination with an activation energy of 48 meV.

PACS 68. 84.60.Jt Cu 2 ZnSnS 4 (CZTS) thin films were prepared by post-annealing films of metal sulfides of Cu 2 S, ZnS and SnS 2 precursors deposited on soda-lime glass substrates by photo-chemical deposition (PCD) from aqueous solution containing CuSO 4 , ZnSO 4 , SnSO 4 and Na 2 S 2 O 3 . In this study, sulfurization was employed to prepare high quality CZTS thin films. Deposited films of metal sulfides were annealed in a furnace in an atmosphere of N 2 or N 2 +H 2 S(5%) at the temperature of 300˚, 400˚ or 500˚C. The sulfured films showed X-ray diffraction peaks from (112), (220), and (312) planes of CZTS and the peaks became sharp by an increase in the sulfurization temperature. CZTS thin film annealed in atmosphere of N 2 was S-poor. After annealing atmosphere was changed from N 2 into N 2 +H 2 S(5%), the decrease of a compositional ratio of sulfur could be suppressed.1 Introduction Cu 2 ZnSnS 4 (CZTS) has a structure obtained by replacing the indium (In) in chalcopyrite CuInS 2 with zinc (Zn) and tin (Sn), and has very suitable optical properties for an absorber layer of solar cell. Firstly, it has a band gap energy of 1.5 eV which is very close to the optimum value of absorber layer of solar cell. Secondly, it has an absorption coefficient over 10 4 cm -1 which is large enough to constitute thin film solar cell. From these significant features, CZTS is expected to be one of the promising materials for thin film solar cell. This material is non-toxic and the component elements are abundant in the crust of the earth and then inexpensive. Therefore, if we can use CZTS film as absorber of solar cells, we will be free from both of the resource saving problem and the environmental pollution. Photo-chemical deposition (PCD), which is employed in this report, is an interesting thin film growth method of a novelty because films can be grown in a short time and at low cost. There are reports in which ZnS, CdS, ZnSe, PbS and CZTS films were deposited by PCD [7][8][9][10][11][12][13].We reported in a previous paper that a CZTS film prepared by PCD and post-annealed at 400˚C was p-type semiconductor and showed photoconductivity and that X-ray diffraction peaks of CZTS were

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Ultra-wideband (UWB) communication is expected to be used for many consumer electronics products in the near future. UWB systems are capable of supporting data rates as high as several hundred Mb/s while consuming a low power. Thus, they are suitable candidates for wireless personal area networks (WPANs). Although UWB systems are allowed to utilize the 3.1-10.6GHz band, first generation UWB systems will probably use the band below 5GHz. A 3.1-5GHz CMOS UWB transceiver is presented in this paper that is based on a direct sequence spread spectrum (DSSS) method as described in reference [1], and is different from 2 merged proposals called MB-OFDM and DS-UWB in the activity of the IEEE 802.15 TG3a [2]. Figure 11.8.1 shows a block diagram of the transceiver. The 8GHz VCO output is divided by 2 to provide 4GHz I and Q signals which are fed to the transmitter block (TX) and the receiver block (RX) as local oscillator (LO) signals, and to the high-speed current-mode logic circuits of the TX pulse modulator as a clock signal.The data, which is spread with a chip rate of 1Gchip/s in the baseband block, enters TX_I and TX_Q, and then the TX pulse modulator performs pulse shaping on each bit. Figure 11.8.2 shows the circuit schematic and simplified timing chart of the TX pulse modulator. The purpose of the pulse shaping is to lower the power density at 3.1GHz, to increase the total transmit power by flattening the spectrum of the transmit signal, and to pre-equalize the waveform of the transmit signal for the RX filter characteristic.In the context of this work, pre-equalization is to perform an approximate reversed-time matched filter of the RX filter as shown in Fig. 11.8.3.The TX pulse modulator in Fig. 11.8.2 allows programmable pulse shaping. The 1GHz Johnson counter has four 1GHz outputs, Q1-4, each shifted by 250ps. Each output is multiplied by a ±1 depending on the polarity of the phase amplitude contribution and the sense of the incoming data bit. The left most multiplier provides a DC offset to the pulse shape. TX_I and TX_Q waveforms are out of alignment with each other by 1ns to perform the π/2-shift BPSK modulation [1]. Outputs Q1-4 and the DC phase are transformed into currents proportional to the signal and the programmable values in the register. The currents are summed, and mixed with LO. The LO Mixer outputs I_OUT and Q_OUT are added up and the resultant signal has an almost constant envelope.The power amplifier has differential output ports whose impedance is 100Ω, and feeds the transmit signal to the antenna through an external balun. The maximum output power is -9dBm and can be set with eight 1dB steps. Figure 11.8.3 shows a measured spectrum of the transmit signal and an analysis result for modulation using a vector signal analyzer. The measured spectrum includes the frequency response of an external balun. The spectrum shows that the transmit signal, without an external band-pass filter, meets the FCC spectrum mask and spreads flat over a wide range centering on 4GHz, although it is slightly inclined. ...