Diode lasers-quantum well

Figure C2.16.ll. Changes in the tlireshold eurrent density of diode lasers resulting from new stRieture eoneepts. A homojunetion diode laser was first demonstrated in 1962. SH and DH stand for single and double heterostaieture, respeetively. The best laser perfonuanee is now obtained in quantum well (QW) lasers.

GaAs, GaAlAs, and GaP based laser diodes are manufactured using the LPE, MOCVD, and molecular beam epitaxy (MBE) technologies (51). The short wavelength devices are used for compact disc (CD) players, whereas the long wavelength devices, mostly processed by MBE, are used in the communication field and in quantum well stmctures. 

R. Cingolani, Optical Properties of Excitons in ZnSe-Based Quantum Well Heterostructures A. Ishihashi and A. V. Nurmikko, II-VI Diode Lasers A Current View of Device Performance... 

S. Nakamura, M. Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, H. Kiyoku, and Y. Sugimoto, InGaN-based multi-quantum-well-structure laser Diodes, Japan J. Appl. Phys. II 35 L74-L81 (1996). 

It was the "quantum well" structure that revolutionized the power output of the diode lasers. This is shown in the following diagram, given as... 

You will note that we have only shown the so-called "quantum wells" of the laser diode. These correspond to the "active layer" of 7.2.27. and 7.2.29. That is, it was found that the "active layer" of the laser could be made much thinner and could be stacked together in the same space as prior diode lasers. It has been determined that, in very thin layers of semiconductors, i.e.- < 20 nm., quantum effects dominate as the electrons become confined. 

This results in the conduction and valence band becoming quantized into "sub-bands or quantum wells. These strained layers result in a vastly improved electrical efficiency as the bicis current is raised in the diode laser. E>en a coherent single array has been improved markedly. The coherent array of 1988 had been improved by 100 times in 2003 while the semi- and incoherent arrays have been improved even more, up to 10 times. What this means is that instead of lining up the arrays as shown in... 

InGaN/GaN QUANTUM WELL HETEROSTRUCTURES GROWN ON SILICON FOR UV-BLUE LASERS AND LIGHT EMITTING DIODES... 

Double-heterostructure lasers are fabricated in form of various stripegeometry laser diodes. Improved production technology allows even the fabrication of single- and multiple-quantum-well lasers [218, 219]. 

The broad spectral coverage for luminescence from the ultraviolet (UV) to the NIR offered via the tunability of composition, size and shape in semiconductor nanocrystals, presents an obvious advantage for the use of such materials as tunable optical gain media, and in laser applications. Furthermore, low lasing thresholds are predicted for QDs and quantum wires, compared with two-dimensionally confined quantum wells, form the basis of the present semiconductor diode laser devices which are ubiquitous in information and telecommunication technologies [86, 87]. 

Many modern semiconductor devices comprise alternating layers of different materials forming superlattices and multiple quantum wells. One well-known example of such structures is the diode laser, a mass-produced device. This device depends on confinement of charges in the two-dimensional structures for enhanced laser output at lowered current thresholds. Such alternating semiconductor layers are usually manufactured either by chemical vapor deposition or by molecular beam epitaxy. The thickness of the layers can be closely controlled in both techniques. As mentioned earlier, electrodeposition also allows good control of thickness. 

Printed circuit board (PCB) A board of electrically insulating material on which has been deposited (printed) conductors that electrically interconnect devices mounted on the board. Almost all electronic systems that consist of more than a few devices utilize one or more PCBs for packaging the electronic system. Quantum well The region of a laser diode where the density of electrons is very high, resulting in increased lasing efficiency and reduced heat generation. 

Another method of increasing the modulation bandwidth is to decrease the photon lifetime. This is most easily accomplished by decreasing the laser diode cavity length. This, however, increases the laser threshold current level, and as a result, lasers with extremely low threshold current levels are required for this method. Utilizing a 40-/rm-long AlGaAs multiple quantum well laser, a modulation bandwidth of 50 GHz has been achieved. 

General Motors Research Laboratories (GMR). Molecular beam epitaxial (MBE) growth of Pbi xEuxSeyTei y lattice-matched to PbTe substrates has been used to fabricate double heterojunction diode lasers, including quantum well, large optical cavity (LOG) devices, the first such TDL structures reported for a lead-salt compound. These Mesa stripe... 

D. L. Partin, "Lead Salt Quantum Well Diode Lasers", Superlattices and Microstructures, 1, 131 (1985). 

C. Freed, J. W. Biellnski, W. Lo, and D. L. Partin "Output Characteristics of Lead-Tellurlde Quantum-Well Diode Lasers", paper presented at the IQEC 84 Conference, Anaheim, CA, 21 June 1984. 

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