Enhanced Optical Emission from GaN Film Grown on Composite Intermediate Layers
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ABSTRACT GaN films have been grown on silicon-(001) substrate with specially designed composite intermediate layers consisting of an ultra-thin amorphous silicon layer and a GaN/AlxGaI.•N (x=0.2) multilayered buffer by metal-organic chemical vapor deposition and characterized by photoluminescence and x-ray diffraction spectroscopy. It was found that the GaN films grown on the composite intermediate layers gave comparable or slightly stronger optical emission than those grown on sapphire substrate under identical reactor configuration. Moreover, the full width at half maximum for the GaN band-edge-related emission is 40 meV at room temperature. This fact indicates that, by using the proposed composite intermediate layers, the crystalline quality of GaN-based nitride grown on a silicon substrate can be significantly improved. INTRODUCTION Recently there has been successful demonstration of commercially available blue and green light-emitting diodes (LEDs)I and long life-time laser diodes (LDs)2 fabricated from group-III nitrides which are generally grown on sapphire substrate. However, besides the large difference in lattice constant and thermal expansion coefficient between the group-III nitride and sapphire substrate, sapphire is an insulating material and extremely rigid. Therefore, it is not easy to fabricate a group-Ill nitride-based semiconductor device on a sapphire substrate. Silicon is one of the proposed substrate materials to overcome this shortcoming because of its high crystal quality, large area size, low manufacturing cost, and the potential application in integrated optoelectronic devices. However, due to the even larger differences in lattice constant and thermal expansion coefficient between the group-III nitride and silicon as compared with sapphire, it is really difficult to grow high quality epitaxial layer of group-III nitride on a silicon substrate. Attempts have been made to grow group-III nitrides on silicon substrates in the past decade using various kind of materials as the intermediate layer between group-III nitride and silicon substrate. These include AIN, 3,4 carbonized silicon,5, 6 nitridized GaAs,7 oxidized AlAs,8 and y-A120 3 .9 In particular, by using AIN thin film as the intermediate layer, ultraviolet and violet-light emitting diodes of group-III nitride have been fabricated on a silicon substrate by molecular beam epitaxy (MBE) recently.3 However, the turn-on voltages as well as the brightness of these diodes do not approach the performance levels of the corresponding devices grown on a sapphire substrate by metal-organic vapor phase deposition (MOCVD). Therefore, both the constitution of the intermediate layer and the growth method for it need to be further optimized in order to enhance the crystallinity of the group-Ill nitrides. In this letter, we report the growth of high quality GaN epitaxial layers on a silicon substrate by MOCVD using the specially-designed composite intermediate layers (CILs). 301 Mat. Res. Soc. Symp. Proc. Vol. 572 01999 Materials Research Society
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