Solid state detector photodiode array

A photomultiplier tube is a sensitive detector of visible and ultraviolet radiation photons cause electrons to be ejected from a metallic cathode. The signal is amplified at each successive dynode on which the photoelectrons impinge. Photodiode arrays and charge coupled devices are solid-state detectors in which photons create electrons and holes in semiconductor materials. Coupled to a polychromator, these devices can record all wavelengths of a spectrum simultaneously, with resolution limited by the number and spacing of detector elements. Common infrared detectors include thermocouples, ferroelectric materials, and photoconductive and photovoltaic devices. 

The optical multichannel photodiode array most used in Raman spectroscopy is the IPDA consisting of a one-dimensional array of amplified photodiodes. The mechanism behind the IPDA detection is that each photodiode converts photons to separated electron-hole pairs (semiconductor-amplification device). In some solid-state detectors (e.g.,... 

For the precise and quick measurement of radiant intensities but also of ion currents photoelectric techniques are used almost exclusively. The measurements can easily be automated. The detectors used are photomultipliers, electron multipliers, photodiode array detectors, camera systems and other solid state detectors. 

A wide variety of solid-state detectors consisting of multiple elements (multiple channels) have been developed over the past 20 years (140). Devices that fall into this category include silicon photodiode (SPD) arrays, charge injection devices (CID), charge coupled devices (CCD), microchannel plate (MCP) image inten-... 

An example of a solid state detector is the Reticon self-scanning photodiode array, which was specifically designed for spectroscopic applications [104]. These diode arrays contain 512 or 1024 silicon diode sensor elements on 25 jum centers corresponding to a density of 40 diodes mm" . Each diode is 2.5 mm high giving each element a slit-like geometry with a 100 1 aspect ratio. Beam registration problems do not apply to the diode array since the channel dimensions are defined by a photomask and hence the detector element size and position are completely reproducible. Solid state detectors do not suffer from lag [105] and althou they will bloom, the effect is much less severe than in a vidicon. 

Detection is normally done with photomultiplier tubes, or, for instruments that incorporate echelle-grating based polychromators, with solid state detectors consisting of a two-dimensional array of photodiodes. 

The common detector for AAS is the photomultiplier tube (PMT). The construction and operation of a PMT has been described in Chapter 5. While PMTs are the most common detectors, solid-state single and multichannel detectors such as photodiode arrays (PDAs) (discussed in Chapter 5) and charge-coupled devices (CCDs) (discussed in Chapters 5 and 7) are increasingly being nsed in AAS spectrometers. Many small systems, particularly those dedicated to one element snch as a dedicated CVAAS mercury analyzer, use solid-state detectors instead of PMTs. Multielement simnltaneous AAS systems also use multichannel solid-state detectors to measure more than one wavelength at a time. 

The detectors in common use for these systems are the PMT or solid-state detectors such as CCDs and charge injection devices (CIDs). PMTs and photodiode arrays (PDAs) are discussed in Chapter 5. More detailed discussion of solid-state detectors is covered in Section 7.2. 

Although most experts predict that third generation self-scanned solid state imagers will eventually become the OIDs of choice, at the present time, their compromised performance, low manufacture yield and therefore, limited commercial availability, greatly limit their use as spectrometric detectors. An exception to that are self-scanned photodiode arrays. 

The classical silicon photodiode linear array manufactured by Reticon was the first detector marketed successfully. Similar solid state linear array detectors based on charge coupled devices, or charge.injection devices may also be of interest. Typical of the families of detectors, the Reticon detectors are built in a number of elements/array sizes. Commercially available units have anywhere from 128 to 1024 elements/array. Each individual element in the array is 1 x 1 mil to 1 x 100 mil in area, and are spaced on approximately 1 mil centers. The spectrometer system discussed in this article was built using Reticon-type devices. 

Another kind of linear solid state position sensitive detectors are the Photo-Diode-Arrays (PDA s), which are different from CCD s. A PDA consists of an array of separate photodiodes, each with an associated capacitance and a multiplexing read-out system (see Fig. 21). The charges collected in each cell are simply switched to the output, one by one. Unlike in the case of CCD s, the photosensitive elements are separated completely from the transfer circuity. 

Silicon charge coupled devices (CCDs), commonly used in solid-state video cameras and in research applications, are being applied to low light level spectroscopy applications. The main advantage of area array CCDs over linear photodiode detectors is the two-dimensional format, which provides simultaneous measurements of spatial and spectral data. 

Phosphor flat panel detector systems (Fig. 2.9) are based on a large-area glass plate. Using solid-state manufacturing techniques, a rectangular array of light-sensitive photodiodes is deposited onto the plate. These... 

---