Metal-Organic Research for Semiconductor Epitaxy


MORSE - 5031

Keywords III-V materials, metal-organic precursors, epitaxial growth methods, MOVPE, CBE


Start Date: 01-JAN-90 / Duration: 36 months

[ contact / participants ]


Objectives and Approach

The MORSE project aims to develop novel non-toxic precursors and to test their quality by MOVPE and CBE. The overall objectives were to:

Progress and Results

Precursors for epitaxy of III-V materials and heterostructures

Safer phosphorous and arsenic precursors for III-V epitaxy are highly desirable due to toxicity, storage and safety problems arising when using phosphine (PH[3]) and arsine (AsH[3]) in MOVPE and CBE. Alternative new liquid organic precursors have been synthesised and characterised. Studies on biphosphinoethane (BPE) or tertiary-butyl phosphine (TBP) and tertiary-butyl arsine (TBAs) led to the conclusion that state-of-the-art, highly uniform MQW laser structures can be grown using these much safer precursors.

When using conventional metal-organic precursors of aluminium (TEAl or TMAl), both the oxygen and the carbon uptake limit the purity of AlGaAs materials grown either by MOVPE or CBE. Diethyl-aluminium-hydride-trimethylamine (DEAlH-NMe[3]) appears to be the best-suited new Al precursor, with higher vapour pressure than TEAl (x 5), and low carbon and oxygen contamination when tested in CBE.

Trimethylindium (TMI) and triethylindium (TEI) are the standard In precursors in MOVPE and CBE. TMI is an explosive-prone solid, and TEI suffers from stability problems. Studies concentrated on dimethylaminopropyl-dimethyl-indium (DADI). This compound, synthesised by Merck, is a promising candidate, being liquid at room temperature and having a high vapour pressure, comparable to that of TEI. High-quality InP has been reproducibly grown with best low temperature mobilities of µ(77 K) > 110 000 cm{2}/Vs.

Metal-organic molecular-beam epitaxy

Preliminary experiments have been conducted on the growth of GaInP with TBP. As observed in the case of InP, carbon concentrations are strongly reduced by using TBP instead of PH[3]. No significant difference is noted for the sulphur, silicon and oxygen levels.

High n-type doping of CBE GaAs and GaInP has been successfully achieved using concentrated sources of disilane and hydrogen sulphide. Thanks to its higher incorporation efficiency with lower memory effect, H[2]S is preferred to Si[2]H[6] as n-type dopant for both GaAs and GaInP. At normal growth temperatures, the sulphur diffusion length is at least as low as the SIMS resolution, ie about 50 Å. This confirms the suitability of H[2]S as an n-type gaseous doping source in CBE of III-V materials for device applications.

An ultra-high level GaAs p-type doping capability has also been established using the TMGa precursor for specific application to the base region of the HBT device. Hole concentrations as high as 1.5 x 10{20} cm{3}, coupled with the lowest reported base contact resistance of 0.013 mm, have already been successfully achieved.

CBE-grown GaAs/GaInP HBT structures have been processed using the standard technology developed within the AIMS project (5032) for GaInP/GaAs MOVPE structures. Considering the high doping level of the base (4.10{19} cm{3}) associated with a very low base resistance, a very satisfying current gain of 40 has been measured for current densities of about 1 kA/cm{2}. Ideality factors for base-collector and base-emitter of respectively 1.1 and 1.05, and with breakdown voltages higher than 5 V for the base-collector junction, are consistent with the DC characteristics of MOVPE GaInP/GaAs HBT structures.

The GaAs/GaAIAs CBE growth and doping capability has therefore allowed initial HBT device structures to be successfully grown and fabricated, and has already yielded very encouraging DC and RF data, even from non-optimised structures. DC current gains measured to date on 100 micron x 100 micron emitter devices have been as high as 40, whilst collector-base breakdown voltages up to 10 V, in excellent agreement with that theoretically expected for the specific structures studied, have also been recorded. RF measurements on 3 x 30 micron emitter devices have already yielded F[T] values as high as 23 GHz (0.13 micron base width), with a corresponding output power of 9.8 Wmm{-1} at 10 GHz. These RF power results represent the first such data ever reported for CBE-grown HBT structures.

Modulated mass spectroscopy studies concerning chemical reactions on the growth surface are in progress.

0.98 micron GaInP/GaAs/GaInAs broad-area lasers have recently been grown by CBE. A CW output power of 600 mW has been measured at 25 °ree;C, without facet coating, and for devices with 100 x 300 micron cavities: this output power is the highest so far reported for this type of device, and is twice that currently achieved by GaAlAs/GaAs/GaInAs lasers of similar design.


CONTACT POINT

Mr Jean-Pierre Hirtz
THOMSON-CSF/LCR
Domaine de Corbeville
F - 91404 ORSAY CEDEX
tel: + 33/ 1-60197340
fax: + 33/ 1-60197829
telex: 204780 TCS F

Participants

THOMSON-CSF/LCR - F - C
CNET - F - P
DRA (DEFENCE RESEARCH
ESTABLISHMENT) - UK - P
FORTH RESEARCH CENTRE - GR - P
RWTH AACHEN - D - P
UNIVERSITÄT STUTTGART - D - P
CNR-PADOVA - I - A
SMI - F - A
ISA RIBER - F - A
ENSSPICAM - F - A


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MORSE - 5031, December 1993


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html version of synopsis by Nick Cook