Use of triethylindium and bisphosphinoethane for the growth on InP by chemical beam epitaxy

Albert Chin, Paul Martin, Utpal Das, John Mazurowski, Jim Ballingall
1992 Applied Physics Letters  
We have demonstrated the first CBE growth of InP using bisphosphinoethane as a group V source. Mirrorlike surface morphology and excellent reflection high-energy electron diffraction patterns were observed. Room temperature and 77 K Hall mobilities for a 2.0 pm thick InP epitaxial layer were 4200 and 22 000 cm'/V s, with carrier densities of 5.7~ 1015 and 4.0~ 1015 cms3, respectively. Although a high n-type impurity concentration is observed at the epitaxial layer-substrate interface, the
more » ... ial layer background impurity concentration is low enough for device fabrication. The full width at half maximum linewidth of the dominant donor bound exciton is 0.84 meV. High quality InGaAsP and all its ternary and binary parent compounds are routinely grown by using gas-source molecular beam epitaxy (GSMBE),' chemical beam epitaxy (CBE) ,2 and metalorganic chemical vapor deposition (MOCVD) .3 Unfortunately, a major obstacle to the eventual production of these materials is the use of the highly toxic compounds AsH3 and PH3. Other disadvantages of PH3, in particular, are its pyrophoric nature and high temperatures required for pyrolysis. The development of new nontoxic organo-metallic sources for PH3 is urgently needed. Tertiarybutyl phosphine (TBP) is an attractive alternative due to its low toxicity (LC,a > 1100 ppm) and excellent InP growth by MOCVD.4 Its application in CBE, however, has not yielded films with comparable purity.' Another difficulty is the high vapor pressure of TBP in a liquid nitrogen cooled CBE chamber. We have observed that the chamber pressure builds to the lop3 Torr level during growth, limiting the practical epilayer thickness. A possible solution to these problems is bisphosphinoethane (BPE, PH,-CHz-CH,-PH*), a low vapor pressure (17.5 Torr at 20 "C) phosphine substitute. BPE also has only one carbon per phosphorus atom and decomposes by releasing the PH, units, leaving a stable C$H, unit. High quality InP and laser diodes have already been demonstrated by BPE using MOCVD.56 In this work we report, what is to our knowledge, the first CBE growth study of InP using BPE. Our samples were grown in a Vacuum Generators V80H molecular beam epitaxy system (MBE) with diffusion-pumped chamber and a custom gas manifold. Both the group III and the group V metalorganics were introduced into the MBE system by means of H, carrier gas flow and down stream pressure control. The samples were grown on semi-insulating Fe-doped InP at substrate temperatures of 450-480 "C, as measured by infrared pyrometry. Typical growth rates for InP were 1.0 pm/h, as measured by reflection high-energy electron diffraction (RHEED) oscillations. In situ mass spectroscopy was used to monitor BPE decomposition. With the cracker at temperatures up to 300 "C the mass spectrum was invariant and showed only the fragmentation of the BPE molecule inside the mass spectrometer. This spectrum served as a reference, allowing us to separate decomposition effects inside the cracker and fragmentation effects inside the mass spectrometer. We find that all the phosphorus species show a sharp increase as we increase the cracker temperature above -400 "C. At -400 "C, cracking of the parent molecule begins. The total amount of free phosphorus increased with cracker temperature up to 800 "C. The decomposition chemistry and the cracker temperature dependence of fragment ratios of C2H,/C,H4 or C,H3/C2H4 shows that the phosphorus species are mainly from the loss of the tirst PH group rather than from both PH groups. This is understandable from the high thermodynamic energy required for the loss of the second PH group. However, that these ratios increase with cracking temperature is an indication the 2nd PH group is being released. More detailed analysis will be presented elsewhere. RHEED reconstruction pattern and RHEED oscillation measurements were performed before each growth to study InP growth dependence on temperature, triethylindium (TEI) flow, and BPE flow. The cracker temperature was set to 650 "C. RHEED oscillations were observed for substrate temperatures above 450 "C. The variation in RHEED oscillations with BPE for a constant TEI flow can be summarized in the following discussion. At 8.0 seem HZ carrier gas flow rate through the BPE bubbler, the RHEED oscillations show a very smooth layer-by-layer two-dimensional growth. At 6.0 seem flow rate, the RHEED oscillation intensity decreases with layer thickness, which is an indication of less perfect-layer-by-layer two-dimensional growth. At 4.0 seem flow rate, the RHEED oscillations only last a few periods. The growth front cannot maintain a smooth growth, and so changes from a layer-by-layer two-dimensional growth to three-
doi:10.1063/1.108491 fatcat:kxtzltpokjhttaruozlq2vjldq