GaAs Epitaxial Growth by ECR-MBE
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GaAs EPITAXIAL GROWTH BY ECR-MBE Naoto Kondo, Yasushi Nanishi, Tomohiro Shibata, Norio Yamamoto and Masatomo Fujimoto NTT Opto-electronics Laboratories, 3-1 Morinosato Wakamiya, Atsugi-Shi, Kanagawa Pref., -43-01 Japan ABSTRACT Electron-cyclotron-resonance plasma-excited molecular beam epitaxy (ECR-MBE) is a new technique for GaAs growth. This paper describes surface cleaning of GaAs and Si substrates at fairly low temperatures using hydrogen plasma, low temperature growth of GaAs on both substrates, and selective area growth of GaAs on both substrates partially covered with a silicon nitride (SiN) mask. The ability to clean and grow at low temperatures-assumed to be a benefit of using energetic particles-should permit us to grow layers on processed GaAs and/or Si substrates. The electrical properties of grown layers are also described. Selective area growth has been successfully carried out with no deposit on the mask or irregular growth at the mask edge. The desorption process introduced by impinging ions is found to play an important role in the selective area growth. INTRODUCTION The application of an ion-beam or plasma-assisted technology to crystal growth offers a particularly attractive strategy for realizing low-temperature processes and the artificial modification of growth kinetics. Low-temperature processes involve a surface cleaning prior to growth, the crystal growth itself and a selective area or recur growth. However, it must be remembered that semiconductors are easily damaged by the bombardment of high energy ions in such applications. Among the various types of plasma generation, ECR plasma has distinct advantages for compound semiconductor growth: it can be sustained in a high vacuum without fil ament or electrodes, both possible sources of contamination, and can generate a sufficient amount of relatively low-energy ions. The energy of impinging ions on the substrate surface has been measured by Matsuoka and Ono' with ECR-plasma equipment. The energy distributions existed in the very low-energy region, around 10-30 eV, at a chamber pressure of 4.5 x 10-1 Torr without the high energy tails usually observed in RF-sputtering. This coherent low-energy scheme is an unique feature of ECR-type plasma source. With these advantages in mind, ECR-MBE was developed in 1987 as a new technique for GaAs growth, by attaching an ECR plasma source to an ultra high vacuum MBE chamber. This 2 ECR-MBE technique was successfully applied to low-temperature growth on Ga~s -5 and 6 8 Si - substrates including low-temperature surface cleaning, low-temperature selective9 2 3 area growth on GaAs -1 and Si substrates1 partially covered by a SiN mask. The Chang et al.14 report of the effectiveness of hydrogen plasma exposure on etching semiconductors and their oxides was followed by extensively investigation of methods using hydrogen ion or plasma: remote plasma processes, ', 6 ion bombardment,' 7 RFplasma related techniques' 8 and ECR-plasma related techniques5'7,8.1 9- 24 , the last because of their low-energy and coherent
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