Tham khảo tài liệu 'the materials science of thin films 2011 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | w hJ ENERGY GAP IN ELECTRON VOLTS AIP OAIP -- GaP GaP AlAs ----- . . AISb GaAs InP ----- GaSb -InAs 0 6 0 _ RK. TIEN5 5 Ị 8. InSb 111 6 200 WAVELENGTH IN MICRONS 5 7-15. Energy gaps and corresponding lattice constants for various compound semiconductors. Courtesy of p. K. Tien AT T Bell Laboratories. . Epitaxy of Compound Semiconductors 329 Figure 7-16. Electron microscope lattice image of GaAs-AlAs heterojunction taken with 100 illumination. From Ref. 13 . Courtesy of JOEL USA Inc. Therefore the correct value for eV. In addition the index of refraction n required for light-guiding properties varies as Ref. 15 n x - X2. 7-12 In summary it is possible to design ternary alloys with Eg larger than GaAs with n smaller than GaAs while maintaining an acceptable lattice match for high-quality heterojunctions. This unique combination of properties has led to the development of a family of injection lasers light-emitting diodes and photodetectors based on the GaAs-AlAs system. . Additional Applications . Optical Communications. Optical communication systems are used to transmit information optically. This is done by converting the initial electronic signals into light pulses using laser or light-emitting diode light sources. The light is launched at one end of an optical fiber that may extend over long distances . 40 km . At the other end of the system the light pulses are detected by photodiodes or phototransistors and converted back into electronic signals that in telephone applications finally generate sound. In such a system it is crucial to transmit the light with minimum attenuation or low optical loss. Great efforts have been made to use the lowest-loss fiber possible and minimize loss at the source and detector ends. If optical losses are high it
