Beryllium bis(cyclopentadienyl), or beryllocene, Be(C5H5)2 (BeCp2) has been used as a CVD precursor for Be-containing layers.
Beryllocene is a monomer in solid with „Slipped-Sandwich“ configuration, in which one Cp-ring has η5-bonding and the second η1-bonding to the central atom. The explanation ist that the optimal η5-Cp-Be bonding distance is smaller than the half of Van-der-Waals-distance between Cp-rings [94, 95, 97, 98]
BeCp2 was applied as a precursor for the MOCVD growth of thin films. of Be metal. Problems with this precursor are extreme air sensitivity and carbon and oxygen incorporation. [4]
Beryllium bis(methylcyclopentadienyl) Be(MeCp)2
Be(MeCp)2 has been considered as one of the best beryllium CVD precursor, f.e. the doping efficiency of (MeCp)2Be of InGaAs layers was reported to be one order of magnitude higher than that of diethylzinc (DEZn).
Be(MeCp)2 for Be-doped InGaAs by MOVPE
Thus, highly Be-doped InGaAs layers with specular surface morphology have been grown, with a hole concentration exceeding 1019 cm-3 after optimization of deposition conditions. InGaAs Be-doping level increases with increasing growth temperature in the temperature range from 570 to 625°C. (MeCp)2Be is promising precursor as p-type dopant source for optoelectronic devices. [[i]]
Be(MeCp)2 for Be-doped InP by MOVPE
Be(MeCp)2 has been applied for the growth of Be-doped InP films by MOCVD and MOMBE [4] The hole concentration reached 1017–1018 cm−3 range and was proportional to the (MeCp)2 Be beam pressure. Be-doped InP films had mirror surfaces regardless of the hole concentration. Comparison of the hole concentration with the Be concentration indicated that the electrical activity of the Be atoms is close to unity. Small amount of carbon atoms incorporated to the film, but no oxygen was found by SIMS. A MQW laser with a Be-doped InP cladding layer has been fabricated, it had threshold current density of 0.6 kA/cm2 for 300 μm cavity. [[ii]
With Be(MeCp)2 as dopant precursor, very good control of Be doping of InP has been obtained, with carrier concentration up to 2×1018 cm-3 achieved keeping excellent surface morphology. The PL peak intensity of the samples was comparable to that of Zn-doped InP. It has been found that Be concentration drops abruptly at the InGaAsP/InP interface in an undoped InGaAsP/Be-doped InP structure, and there is no significant Be diffusion into undoped InGaAsP, indicating that Be is very promising p-type dopant alternative to Zn, which has a large diffusion coefficient in the InP layer, forexample for InGaAsP/InP laser diodes. [[iii]
[i]Suzuki, D.; Kimura, T.; Takiguchi, T.; Takemi, M.; Fujii, S.; Mihashi, Y.; Higuchi, H.;
Indium Phosphide and Related Materials, 1997., Intern Conf on, Issue Date: 11-15 May 1997, On page(s): 540 - 543
[ii]Manabu Mitsuhara, Matsuyuki Ogasawara and Hideo Sugiura, Journal of Crystal Growth, Volume 183, Issues 1–2, 1 January 1998, Pages 38-42, “Beryllium doping of InP during metalorganic molecular beam epitaxy using bismethylcyclopentadienyl-beryllium”
[iii]Tatsuya Kimura, Takao Ishida, Takuji Sonoda, Yutaka Mihashi, Saburo Takamiya, Sigeru Mitsui, Jpn. J. Appl. Phys. 34 (1995) pp. 1106-1108, “ Metalorganic Vapor Phase Epitaxy Growth of Be-Doped InP Using Bismethylcyclopentadienyl-Berylium”