What is the Quantum well laser diodes?
Quantum well laser diode is a type of semiconductor diode that has double heterostructure (DH) where the thickness of the active layer is so narrow ( ≈ 5–20 nm) ≤ de Broglie wavelength of the electron. It is formed when a layer of the low bandgap substrate material with a thickness range ( ≈ 5–20 nm) is sandwiched between the two high bandgap substrate materials. Usually, Gallium arsenide (GaAs) is sandwiched between the aluminum gallium arsenide (AlxGa(1-x)As). The quantum well laser diodes operate at a wavelength range from 630 to 1470 nm. It is available in both free space and fiber-coupled type. These diodes are ideal for material Processes, solid State laser excitation, medical Use, measurement, sensor, and industrial optical module applications.
The quantum confinement (electron energy level splitting in potential well) occurs at the narrow active region (GaAs). A Quantum well is the potential well that has electron energy level split apart by milli-electron volts. This quantum well structure modifies the electronic and optical properties of the semiconducting materials. The structure allows a large number of radiated transitions between discrete energy levels than in the conventional double heterostructure laser diodes. Hence, the efficiency of the quantum well laser diode is more than the conventional DH laser diodes.
The wavelength of the laser light from a quantum well laser diode is based on the width of the narrow active region only. But, in a normal laser diode (homojunction diode), the wavelength of the light can only be varied by varying the material compositions (difficult process). Besides, the alteration in the density states of the semiconductor (i.e., electron energy levels splitting) helps to reduce the threshold current rating of a quantum well laser diode (because of the narrow bandgap). The quantum well laser diodes are less sensitive to temperature variations because the carrier distribution in the quantum well is much less sensitive to temperature.
Quantum well laser diode
Band gap of Quantum well laser diode
LASER DIODE INTRODUCTION IS GIVEN BELOW:
A laser diode is a type of optoelectronic device that converts electrical energy into laser light energy by stimulated emission principle. The structure of the laser diode consists of a highly reflective surface at one end, and another partially reflective surface on the opposite end forms the optical cavity that amplifies the laser energy. Mostly, the semiconducting material GaAs, GaN, and InP are used in the fabrication of laser diodes.
Simple laser diode
The laser diodes can emit laser light from the UV region to the infrared region. The wavelength of the laser diodes depends upon the type of material and its compositions. The output power range of the laser diodes can vary from milliwatts to several kilowatts. Different types of laser diodes are available. Quantum well laser diode is the one type of laser diode.
A simple laser diode is a homojunction laser diode. Homojunction means that the junction between two similar semiconductor materials that have equal band gaps but with different doping. Mostly, the homojunction laser diodes or the simple laser diodes are not suitable for optical communication. Because they could not able to confine locations of light as well as current carriers very well. Hence, the efficiency of the homojunction diode is low. Also, homojunction diodes need a high threshold current.
Today modern applications (e.g. optical communication) need high-efficiency laser diodes. Hence, to meet the requirements of modern applications, the structure of simple laser diodes discussed above modified in recent years that results in various types of laser diodes available today. For example, Double heterostructure laser diodes, quantum well laser diodes, multi-quantum well laser diodes, and vertical-cavity surface-emitting laser diodes.
Specifications details of quantum well laser diodes:
Central wavelength: Represents the wavelength of laser emitted from the quantum well laser diode. The wavelength is represented in nm (nanometre). The quantum well laser diodes can have a wavelength range from 630 to 1470 nm.
Technology: Quantum well
Operation mode: Represents the operation mode CW mode/Pulse mode.
Type: Free space / Fiber-coupled
Output power: Represents the output power of the quantum well laser diode. The quantum well laser diodes are available in the power range from 3 mW to 6000 W.
Threshold current (Ith): It is the current at which the output optical power increases sharply. When the laser diode is biased below this threshold current, the output optical power will be very low. It is represented in x A. The threshold current is proportional to the output power. Mostly, the quantum well laser diodes have the threshold current range of 0.5 mA to 80 mA, and some quantum well diodes can have the threshold current range from 1 A to 24 A.
Vertical Divergence Angle (θ⊥): The angle at which the light-emitting band spreads in a direction vertical to the PN junction. It is usually in the range of 15˚- 40˚.
Horizontal Divergence Angle (θ∥): The angle at which the light-emitting band spreads in a direction parallel to the PN junction. Typically, it is in the range of 6˚-10˚.
Operating current: It is the driving current or input currents when the quantum well laser diode reaches the rated power. It is represented in x A. The operating current is proportional to the output power.
Operating voltage: Represents the supply voltage. Usually, it is in the range from 1.5 to 2.8 V.
Reverse voltage: Represents the maximum allowable reverse voltage, when it is applied across the laser diode. Beyond the reverse voltage, the diode will damage. It is usually in the range of 2 V.
Laser gain medium: Represents the semiconducting material used in the active or gain medium. The InGaAlP, AlGaAs, and GaAs are usually used as the gain medium.
Operating temperature: Represents the safe operating temperature of the quantum well laser diode. Typically, it has a range of -10 °C to + 60 °C.
Storage temperature: Represents the storage temperature range of quantum well laser diode. Typically, it has a range of -40 °C to + 85 °C.
Package type: Represents the type package used to pack the quantum well laser diodes. Usually, the quantum well laser diodes are available in TO-can, C-mount,sub-mount, bar, through-hole, butterfly packages.