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Metal nanoparticles (NPs) are well known to increase the efficiency of photovoltaic devices by reducing reflection and increasing light trapping within device. However, metal NPs on top flat surface suffer from high reflectivity losses due to the backscattering of the NPs itself. In this paper, we experimentally demonstrate a novel structure that exhibits localized surface plasmon resonance (LSPR) along with broadband ultralow reflectivity over a wide range of wavelength. Experimental results show that by depositing Ag NPs and Au NPs onto glass subwavelength structures (SWS) the backscattering effect of NPs can be suppressed, and the reflections can be considerably reduced by up to 87.5% and 66.7% respectively, compared to NPs fabricated on a flat glass substrate. Broadband ultralow reflection (< 2%) is also observed in the case of Ag NPs and Au NPs fabricated on cone shaped SWS silicon substrate over a wavelength range from 200 nm to 800 nm. This broadband ultralow reflectivity of Ag NPs and Au NPs on silicon SWS structure leads to a substantial enhancement of average absorption by 66.53% and 66.94%, respectively, over a broad wavelength range (200-2000 nm). This allows light absorption by NPs on SWS silicon structure close to 100% over a wavelength range from 300 nm to 1000 nm. The mechanism responsible for the increased light absorption is also explained.

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In this paper the optical gain mechanism in phototransistor detectors (PTDs) is explored in low light conditions. An analytical formula is derived for the physical limit on the minimum number of detectable photons for the PTD. This formulation shows that the sensitivity of the PTD, regardless of its material composition, is related to the square root of the normalized total capacitance at the base layer. Since the base total capacitance is directly proportional to the size of the PTD, the formulation shows the scaling effect on the sensitivity of the PTD. We used the extracted formula to study the sensitivity limit of a typical InGaAs/InP heterojunction PTD. Modeling predicts that a PTD with a nanoscale electronic area can reach to a single photon noise equivalent power even at room temperature. The proposed model can also be used to explore the sensitivity and speed of the nanowire-based photodetectors. To the best of our knowledge, this is the first comprehensive study on the sensitivity of the PTD for low light detection.Comment: 5 pages, 5 figure

We report the experimental characterization of high-responsivity plasmonics-based GaAs metal-semiconductor-metal photodetector (MSM-PD) employing metal nano-gratings. Both the geometry and light absorption near the designed wavelength are theoretically and experimentally investigated. The measured photocurrent enhancement is 4-times in comparison with a conventional single-slit MSM-PD. We observe reduction in the responsivity as the bias voltage increases and the input light polarization varies. Our experimental results demonstrate the feasibility of developing a high-responsivity, low bias-voltage high-speed MSM-PD.

We report the effect of different surface treatment and passivation techniques on the stability of InGaAs/InP heterojunction phototransistors (HPTs). An In 0.53 Ga 0.47 As surface passivated with aqueous ammonium sulfide ((NH 4) 2 S), aluminum oxide (Al 2 O 3) grown by atomic layer deposition (ALD), and their combination is evaluated by using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). All samples were kept in the air ambient, and their performances were periodically measured to investigate their long-term stability. Raman spectroscopy revealed that the peak intensity of the GaAs-like longitudinal optical phonon of all passivated samples is decreased compared with that of the control sample. This is attributable to the diminution of the carriers near the passivated surfaces, which was proven by extracted surface potential (V s). The V s of all passivated samples was decreased to less than half of that for the control sample. XPS evaluation of As3d spectra showed that arsenic oxides (As 2 O 3 and As 2 O 5) on the surfaces of the samples can be removed by passivation. However, both Raman and XPS spectra show that the (NH 4) 2 S passivated sample reverts back over time and will resemble the untreated control sample. When capped with ALD-grown Al 2 O 3 , passivated samples irrespective of the pretreatment show no degradation over the measured time of 4 weeks. Similar conclusions are made from our experimental measurement of the performance of differently passivated HPTs. The ALD-grown Al 2 O 3 passivated devices show an improved optical gain at low optical powers and long-term stability. Published by AIP Publishing.

Integration of an InGaAs/InP quantum well infrared photodetector (QWIP) onto a Si substrate was successfully demonstrated via a metal-assisted wafer bonding (MWB) using a Mo/Au metal scheme. The Mo/Au/Mo layer, situated between the QWIP structure and the Si, has shown a well-ordered lamination. It provides a smooth surface with a roughness of about 0.8 nm, as measured by a scanning electron microscope (SEM) and atomic force microscopy (AFM). The results on crystalline quality evaluated by Raman spectroscopy and X-ray diffraction (XRD) imply that the MWB could be achieved without any measurable material degradation and residual strain. Temperature dependence of dark current revealed that there is no noticeable change in the dark current properties of the QWIP after bonding on Si, despite that the quantum wells are only 200 nm away from the bonding interface.

We propose and numerically demonstrate a high absorption hybrid-plasmonic-based metal semiconductor metal photodetector (MSM-PD) comprising metal nanogratings, a subwavelength slit and amorphous silicon or germanium embedded metal nanoparticles (NPs). Simulation results show that by optimizing the metal nanograting parameters, the subwavelength slit and the embedded metal NPs, a 1.3 order of magnitude increase in electric field is attained, leading to 28-fold absorption enhancement, in comparison with conventional MSM-PD structures. This is 3.5 times better than the absorption of surface plasmon polariton (SPP) based MSM-PD structures employing metal nanogratings and a subwavelength slit. This absorption enhancement is due to the ability of the embedded metal NPs to enhance their optical absorption and scattering properties through light-stimulated resonance aided by the conduction electrons of the NPs.