Analysis of the mixing effect in InAlAs/InGaAs metal‐semiconductor‐metal photodetectors

Abstract

MHz is also obtained. The impedance bandwidth is 350 MHz (1710( -2060, covering the required bandwidths of the DCS and PCS bands. Figure 2(b) shows the measured return loss for three possible values of ␣ ϭ 15°, 25°, 35°. Relatively very small effects on the lower operating band are seen. On the other hand, the bandwidth of the upper operating band increases with an increase in ␣. The obtained results indicate that, for possible values of ␣ for the mobile phone in the talk condition, the proposed antenna is capable of covering the operating bandwidths of the GSM, DCS, and PCS bands.The radiation characteristics of the constructed prototype were also studied. Figures 3, 4, and 5 plot the measured radiation patterns at the center frequencies 925, 1795, and 1920 MHz, respectively, of the GSM, DCS, and PCS bands for the condition with ␣ ϭ 15°. The results for other conditions with ␣ ϭ 25°and 35°were also measured, and no special distinction in the measured radiation patterns was observed. In addition, other operating frequencies across the GSM, DCS, and PCS bands were also measured and showed similar patterns as plotted here. Measured antenna gain for the proposed antenna with ␣ ϭ 15°in the lower band for GSM operation and in the upper band for DCS/PCS operations is shown in Figure 6(a) and (b). The antenna gain obtained is about 0.8 -1.4 dBi across the GSM band, and that for the DCS/PCS bands is in a range of about 1.6 -2.6 dBi. CONCLUSIONA novel internal planar monopole antenna suitable for application in folder-type mobile phones for GSM/DCS/PCS operation has been proposed, and a constructed prototype have been studied. The proposed antenna is easy to implement and can be constructed at low cost. In addition to its compact structure (occupying a small area of 10 ϫ 40 mm 2 only), the proposed antenna shows good radiating characteristics for operating frequencies across the GSM, DCS, and PCS bands. InGaAs MSM-PDs would allow LADAR operation at eye-safe wavelengths, mainly 1.55 m. Unfortunately, the Schottky barrier height on InGaAs is quite low (ϳ0.1-0.2 eV) [5] leading to high dark current and, hence, low signal-to-noise ratio. To reduce dark current, various methods of "enhancing" the Schottky barrier have been used. The most commonly used method employs high-bandgap lattice-matched InP [6] or InAlAs [7,8] Schottky enhancement layers (SELs). Detectors using SELs yield low dark current, high responsivity, and high bandwidths.In this paper we analyze the optoelectronic mixing effect in an InAlAs Schottky-enhanced InGaAs MSM-PD. We find that the frequency bandwidth of such an OEM is less than that of a photodetector. We also show that the mixing efficiency depends on both the RF, LO, and IF frequencies and decreases nonlinearly with decrease in optical power. We attribute this behavior to the band-gap discontinuity associated with the SEL and present a circuit model of the OEM to explain the experimental results. EXPERIMENTThe MBE-grown InGaAs MSM-PD consists of a 500-Å InAlAs SEL, a 250-Å In(Ga,Al)As graded layer...

Design of Transparent Indium Tin Oxide-Based Interdigitated Fingers for Metal Semiconductor Metal Photodetector

“…14 However, studies of the optimal geometric design of transparent ITO finger MSM photodetectors have not been reported to date. The optimized designs employed for the more conventional metal-based interdigitated fingers 15,16 are not suitable for the ITObased transparent contacts due to the absence of shadowing effects in the latter case.…”