| 21. |
- Jain, Vishal, 1989-, et al.
(author)
-
Large Area Photodetectors at 1.3/1.55 μm Based on InP/InAsP NWs
- 2014
-
Conference paper (peer-reviewed)abstract
- Optical communication systems benefit a lot from APDs due to their increased photocurrent gain as compared to conventional photodetectors. An avalanche region in a high bandgap material is especially useful to avoid the tunneling leakage currents in smaller bandgap materials needed for absorption at 1.3/1.55 µm wavelengths. Self-assembled III-V semiconductor nanowires have a key advantage owing to the enhanced absorption due to optical resonance effects and the strain relaxation in NWs, thus facilitating monolithic integration of different heterostructures on cheaper substrates. Here, we present electrical and optical results from large ensembles of InP/InAsP NWs, axially grown on p+ InP substrates. The NW base consists of an InP p-n junction acting as the avalanche region followed by an InP/InAsP absorption region, and ending with a top InP n+-segment. The 130nm diameter NW arrays are contacted in a vertical geometry using SiO2 as the insulating layer and ITO as the top contact. The n-doping in the avalanche region is varied to study it’s influence on the avalanche mechanism. Also the bandgap in the absorption region is varied from pure InP to smaller bandgap InAsP by varying the As content. Clear interband signals from different crystal phases of InP/InAsP are observed in photocurrent spectroscopy. Moreover, the photocurrent spectra are consistent with spatially resolved photoluminescence signals. We also report on polarization and angle dependent photocurrent response of the NW array.
|
|
| 22. |
- Jain, Vishal, 1989-, et al.
(author)
-
Large area photodetectors based on InP NWs with InAs/InAsP QWs
- 2014
-
Conference paper (peer-reviewed)abstract
- Focal plane arrays have a widespread use in infrared imaging, which often rely on cryogenic cooling to curtail the dark current level necessary for a reasonable signal-to-noise ratio. Quantum well (QW) infrared photodetectors are uniform over large areas, but suffer from a severe drawback related to the selection rules for intersubband absorption. An interesting alternative is self-assembled III-V nanowires offering a key advantage owing to the enhanced absorption by optical resonance effects and strain relaxation.We present electrical and optical results from large ensembles of n+-i-n+ InP NWs, axially grown on InP substrates with InAs/InAsP QWs embedded within the i-segment, designed for both interband and intersubband detection. The NWs are contacted in a vertical geometry using 50 nm SiO2 as the insulating layer and ITO as the top contact. We first investigate the crystal quality of the InAsP QWs grown in 180 nm diameter NWs, using PL, CL and TEM. To achieve more abrupt InAs/InAsP QWs, we grow 130 nm diameter NWs and deplete the In present in the Au catalysts. The effect of n-doping on the device performance is studied by fabricating two different NW geometries, with and without an n+-segment grown before the nominal i-segment in the NW. In addition, the position of the QWs within the i-segment is varied to further scrutinize effects related to doping and crystal structure. Finally, we report spectrally resolved photocurrent results from the QWs in the near-infrared region and discuss about the further developments needed for intersubband detection.
|
|
| 23. |
|
|
| 24. |
|
|
| 25. |
|
|
| 26. |
- Karimi, Mohammad, 1988-, et al.
(author)
-
Infrared Photodetectors Based on Nanowire Arrays – Towards Far Infrared Region
- 2017
-
Conference paper (peer-reviewed)abstract
- Nanowire semiconductors are promising candidates for optoelectronic applications such as solar cells, photodetectors and lasers due to their quasi-1D geometry and large surface to volume ratio. The functional wavelength range of NW-based detectors is typically limited to the visible/near-infrared region. In this work, we present electrical and optical properties of novel IR photodetectors based on large square millimeter ensembles (>1million) of vertically processed semiconductor heterostructure nanowires (NWs) grown on InP substrates which operates in longer wavelengths. InP NWs comprising single or multiple (20) InAs/InAsP QDics axially embedded in an n-i-n geometry, have been grown on InP substrates using MOVPE. The NWs are contacted in vertical direction by ALD deposition of 50 nm SiO2 as an insulating layer followed by sputtering of ITO and evaporation of Ti and Au as top contact layer. In order to extend the sensitivity range to the mid-wavelength and long-wavelength regions, the intersubband transition within conduction band of InAsP QDisc is suggested. We present first experimental indications of intersubband photocurrent in NW geometry and discuss important design parameters for realization of intersubband detectors. Key advantages with the proposed design include large degree of freedom in choice of materials compositions, possible enhanced optical resonance effects due to periodically ordered NW arrays and the compatibility with silicon substrates. We believe that our novel detector design offers the route towards monolithic integration of compact and sensitive III-V NW long wavelength detectors with Si technology.
|
|
| 27. |
|
|
| 28. |
- Karimi, Mohammad, 1988-, et al.
(author)
-
Intersubband Quantum Disc-in-Nanowire Photodetectors with Normal-Incidence Response in the Long-Wavelength Infrared
- 2018
-
In: Nano letters (Print). - Washington : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:1, s. 365-372
-
Journal article (peer-reviewed)abstract
- Semiconductor nanowires have great potential for realizing broadband photodetectors monolithically integrated with silicon. However, the spectral range of such detectors has so far been limited to selected regions in the ultraviolet, visible, and near-infrared regions. Here, we report on the first intersubband nanowire heterostructure array photodetectors exhibiting a spectrally resolved photoresponse from the visible to long-wavelength infrared. In particular, the infrared response from 3 to 20 μm is enabled by intersubband transitions in low-bandgap InAsP quantum discs synthesized axially within InP nanowires. The intriguing optical characteristics, including unexpected sensitivity to normal incident radiation, are explained by excitation of the longitudinal component of optical modes in the photonic crystal formed by the nanostructured portion of the detectors. Our results provide a generalizable insight into how broadband nanowire photodetectors may be designed and how engineered nanowire heterostructures open up new, fascinating opportunities for optoelectronics.
|
|
| 29. |
- Karimi, Mohammad, 1988-, et al.
(author)
-
Long-wavelength intersubband quantum disc-in-nanowire photodetectors with normal incidence photoresponse
- 2018
-
In: QSIP 2018. ; , s. 55-55
-
Conference paper (peer-reviewed)abstract
- Semiconductor nanowire (NW) technology has emerged as a key facilitator of novel optoelectronics e.g. solar cells, photodetectors and LEDs. The functional wavelength range of current NW-based photodetectors is typically limited to the visible/ near-infrared region. In this work, we present the first ever reported electrical and optical characteristics of longwavelength IR photodetectors based on large square millimeter ensembles of vertically grown and processed InAsP/InP heterostructure NWs grown on InP substrates1 . More specifically, the MOVPE-grown NWs comprise single or multiple InAsP quantum discs (QDiscs) axially embedded in an n+-i-n+ geometry. The NWs are contacted together in a vertical geometry by uniformly depositing a thin insulating SiO2 layer, selective etching of the oxide from the tip of the NWs followed by sputtering of ITO as a common top contact to all NWs. Using Fourier transform photocurrent spectroscopy, we demonstrate a photoresponse extending from the visible to far infrared1,2. In particular, the infrared response from 3-20 μm is enabled by intersubband transitions in the lowbandgap InAsP quantum discs synthesized axially within the InP NWs. The detector elements exhibit an unexpected sensitivity to normal incident radiation, apparently in contradiction to well-known selection rules for intersubband transitions in quantum wells. From in-depth 2D and 3D optical simulations we attribute this result to an excitation of the longitudinal component of optical modes in the photonic crystal formed by the nanostructured portion of the detectors. Key advantages with the proposed design include a large degree of freedom in choice of material compositions, enhanced optical resonance effects due to periodically ordered NW arrays and the compatibility with silicon substrates. We believe that our novel detector design offers a route towards monolithic integration of compact and sensitive broadband III-V NW detectors with main-stream silicon technology which could seriously challenge existing commercially available photodetectors.
|
|
| 30. |
- Karimi, Mohammad, 1988-, et al.
(author)
-
Nanowire photodetectors with embedded quantum heterostructures for infrared detection
- 2019
-
In: Infrared physics & technology. - Amsterdam : Elsevier. - 1350-4495 .- 1879-0275. ; 96, s. 209-212
-
Journal article (peer-reviewed)abstract
- Nanowires offer remarkable opportunities for realizing new optoelectronic devices because of their unique fundamental properties. The ability to engineer nanowire heterostructures with large bandgap variations is particularly interesting for technologically important broadband photodetector applications. Here we report on infrared photodetectors based on arrays of InP nanowires with embedded InAsP quantum discs. We demonstrate a strongly reduced dark current in the detector elements by compensating the unintentional n-doping in the nominal intrinsic region of the InP nanowires by in-situ doping with Zn, a crucial step towards realizing high-performance devices. The optimized array detectors show a broad spectral sensitivity at normal incidence for wavelengths from visible to far-infrared up to 20 μm, promoted by both interband and intersubband transitions. Optical simulations show that the unexpected normal incidence response at long wavelengths is due to non-zero longitudinal modes hosted by the nanowires. © 2018 Elsevier B.V.
|
|
