In-Situ Etch to Improve Chemical Beam Epitaxy Regrown AlgaAs/GaAs Interfaces for HBT Applications
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possible contamination in the atmosphere. Recently, many research groups have reported studies of in-situ etching of E11-V compounds using different gaseous sources. Mui et al. [3] reported high-quality etched/regrown GaAs interfaces using an in-situ C12 etching process, but a complicated interlocking system of separate growth and etching chambers was used. Also Tappura et al. [4] reported that in-situ cleaning of GaAs surface in MBE using an atomic hydrogen plasma can obtain high quality interfaces. Tsang et al. [5] reported in-situ etching of GaAs and InP using AsC13 and PCI3 prior to regrowth in the same chemical beam epitaxy (CBE) chamber; therefore, possible contaminations in the etched/regrown interface can be minimized. However, C12 decomposed from AsCI 3 or PCI3 is corrosive and may etch filaments in the growth chamber, so the long term use of AsCI3 or PC13 could be a concern. Tateno et al. [6] and Hou et al. [7] found that gaseous carbon doping sources, such as CC14 and CBr 4, can etch GaAs and AlAs in organometallic vapor phase epitaxy (OMVPE), but carbon impurities dissociated from these doping sources during in-situ etching process would contaminate the etched/regrown interface. Therefore, an etching source that has no direct bonds to carbon and halogen (Cl and Br) would be highly desirable. Villaflor et al. found that tris-dimethylaminoarsenic (TDMAAs) has an etching effect on GaAs in a CBE system [8-9]. This TDMAAs with As directly bonded to N is a promising As source. Because there are no As-H bonds, TDMAAs is expected to be less toxic than arsine
87 Mat. Res. Soc. Symp. Proc. Vol. 448 © 1997 Materials Research Society
(AsH3) [10]. Also due to the lack of direct As-C bonds, TDMAAs has been successfully used in metalorganic molecular beam epitaxy (MOMBE)/CBE of (AI,Ga)As with a lower carbon incorporation [11-14]. The objective of this work is to investigate the TDMAAs etched/regrown interface of GaAs and AlGai-xAs for device application. Our results show that improved etched/regrown interfaces and pn junctions can be obtained. These characteristics are important to realize emitter-up HBTs with low emitter-edge recombination, as well as collectorup HBTs. EXPERIMENT The in-situ etching and regrowth experiments were performed in a modified PerkinElmer 425B CBE system. Uncracked TDMAAs was carried by hydrogen and transported into
the CBE chamber through an ultrahigh vacuum leak valve. The H2 flow rate was varied from 2 to 4 sccm to adjust the TDMAAs flux, corresponding to an As incorporation rate of 1.2 to 2.0 monolayer per second (ML/s), as determined from As-induced intensity oscillations of reflection high-energy electron diffraction (RHEED) on a Ga-rich GaAs surface. For the study of etched/regrown interfaces, Si-doped GaAs were regrown twice on n' Si-doped (100) GaAs substrates by using triethylgallium (TEGa), tertiarybutylarsine (TBA) or arsenic (As4), and silicon tetrabromide (SiBr 4) . The regrowth temperature and V/Il ratio were 510°C and 1.3, respectively. Capacitance-voltage (C-V) measurement
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