BOOK_CONTENT
From Photonics Essentials : An Introduction with Experiments

3.1 Introduction

There are a number of solid-state devices that can generate an electric signal when they are illuminated. We can divide all these devices into two categories. In one category are the devices that convert the energy in a beam of light into an electric signal. An example of this is the bolometer. This is really a collection of thermocouples inside an efficient photon absorber. The energy of the photons is converted to heat, and the rise in temperature is converted by the thermocouples into an electric signal. These devices are energy detectors. The electrical current is proportional to the energy in the optical beam. In the second group are quantum threshold detectors. Photons can be absorbed in these devices if the energy of a photon exceeds a certain threshold value. All absorbed photons generate the same current, regardless of their energy above the threshold value. Photodiodes fall into this second category. Photons can be absorbed in a photodiode if their energy exceeds the band gap energy of the photodiode material. In principle, each photon absorbed contributes one electron to the current. This is a direct exchange of quanta one electron for one photon. In most photodiodes, this exchange is nearly 100% efficient.

Photodiode detectors were developed along with the transistor. Silicon is the most common photodiode material for two reasons. Silicon photodiodes are sensitive to a range of light wavelengths that include the region of visible light. Silicon photodiode manufacture benefits from the same advanced processing technology used to...

Copyright The McGraw-Hill Companies, Inc. 2003 under license agreement with Books24x7

Products & Services
Photodiodes
Photodiodes are used for the detection of optical power (UV, Visible, and IR) and for the conversion of optical power to electrical power.
Photosensor Modules
Photosensor modules are compact light detectors with built-in power supplies. They use photomultiplier tubes, avalanche photodiodes, PN photodiodes, or PIN photodiodes.
Fluorometers
Fluorometers measure the amount of fluorescent radiation produced by a sample exposed to monochromatic radiation.
PIN Diodes
PIN diodes are three-layer semiconductor diodes consisting of an intrinsic layer separating heavily doped P and N layers. The charge stored in the intrinsic layer in conjunction with other diode parameters determines the resistance of the diode at RF and microwave frequencies.
Phototransistors
Phototransistors are solid-state light detectors with internal gain that are used to provide analog or digital signals. They detect visible, ultraviolet and near-infrared light from a variety of sources and are more sensitive than photodiodes. This category includes photodarlingtons. 

Topics of Interest

Light detectors perform the opposite function of light emitters. Emitters, as we already know, are electro-optic devices. They convert electrical pulses into light pulses. Detectors are opto-electric...

  Avalanche Photodiode If a small load resistance RLis used to increase the frequency bandwidth of a PIN photo-diode, the signal voltage may be quite small, requiring amplification. This can be...

  Schottky Photodiode The PIN and avalanche photodiodes discussed in the previous two sections are both p-n-junction-based devices. In contrast, the Schottky photodiode utilizes a...

Silicon photodiodes are semiconductor devices responsive to high-energy particles and photons. Photodiodes operate by absorption of photons or charged particles and generate a flow of current in an...

5.3 OPTICAL PROCESSES IN SEMICONDUCTORS In this section we will consider the basic photon absorption and emission processes in semiconductors. To understand the optical processes we need not only to...