T. J. de Lyon

Lattice contraction due to carbon doping of GaAs grown by metalorganic molecular beam epitaxy

Epitaxial layers of GaAs have been grown by metalorganic molecular beam epitaxy (MOMBE) with atomic carbon concentrations ranging from 4×1017 to 3.5×1020 cm−3. The dependences of GaAs lattice parameter and hole concentration on atomic carbon concentration have been determined from x‐ray diffraction, Hall effect, and secondary‐ion mass spectrometry measurements. For atomic carbon concentrations in excess of 1×1019 cm−3, the hole concentrations are less than the corresponding atomic carbon concentrations. Lattice parameter shifts as large as 0.2% are observed for carbon concentrations in excess of 1×1020 cm−3, which results in misfit dislocation generation in some cases due to the lattice mismatch between the C‐doped epilayer and undoped substrate. Over the entire range of carbon concentrations investigated, Vegard’s law accurately predicts the observed lattice contraction.

High carbon doping efficiency of bromomethanes in gas source molecular beam epitaxial growth of GaAs

Carbon tetrabromide (CBr4) and bromoform (CHBr3) have been studied as carbon doping sources for GaAs grown by gas source molecular beam epitaxy (GSMBE) with elemental Ga and thermally cracked AsH3. Hole concentrations in excess of 1×1020 cm−3 have been measured by Hall effect in both CBr4‐ and CHBr3‐doped GaAs, which agrees closely with the atomic C concentration from secondary‐ion mass spectrometry, indicating complete electrical activity of the incorporated carbon. The GaAs growth rate is unaffected by the CBr4 and CHBr3 fluxes over the range of dopant flow investigated. The efficiencies of carbon incorporation from CBr4 and CHBr3 are, respectively, 750 and 25 times that of trimethylgallium (TMG), which is commonly employed as a carbon doping source in metalorganic MBE (MOMBE). The sensitivity of carbon incorporation to varying substrate temperature and V/III ratio has been observed to be significantly reduced with CBr4 and CHBr3 from that obtained under similar growth conditions with TMG in MOMBE.

LVM spectroscopy of carbon and carbon-hydrogen pairs in GaAs grown by MOMBE

Cryogenic (4.2 K) infrared absorption measurements of GaAs films grown by MOMBE and containing a high concentration of carbon acceptors ( approximately 2*1020 cm-3) show an asymmetric Fano resonance at the frequency of the CAs local mode (582 cm-1). After rapid transient annealing at 950 degrees C for 12 s in an atmosphere of helium and arsine, there is a reduction in the hole concentration, and localized vibrational mode (LVM) spectroscopy reveals the presence of nearest neighbour H-CAs passivated pairs. Previously unreported lines at 452.8 cm-1 and 563.0 cm-1 may be due to the vibrations of the passivated carbon atoms, or possibly CGa donors.

Carbon doping of GaP, GaInP, and AlInP in metalorganic molecular beam epitaxy using methyl and ethyl precursors

The group III precursors trimethylgallium (TMG), triethylgallium (TEG), trimethylaluminum (TMA), and triethylaluminum (TEA) have been investigated as intrinsic carbon doping sources for epilayers of GaP, Ga0.51In0.49P, and Al0.51In0.49P grown by metalorganic molecular‐beam epitaxy (MOMBE) using thermally cracked phosphine (PH3). Carbon incorporation in these films has been evaluated with calibrated secondary ion mass spectrometry (SIMS), Hall effect measurements, and capacitance‐voltage (C–V) profiling. The carbon doping properties of TMG and TEG in GaP growth are compared with those observed in MOMBE growth of GaAs. Hole concentrations in excess of 1×1020 cm−3 have been measured in films of GaP grown with TMG/PH3, which is far above that achievable in GaAs grown with TMG/AsH3 under similar growth conditions. Neither TMG nor TEG result in p‐type conductivity in films of Ga0.51In0.49P. At a growth temperature of 500 °C, SIMS measurements indicate that the carbon incorporation is inversely related to the In...

Experimental observation of a minority electron mobility enhancement in degenerately doped p‐type GaAs

The variation of minority electron mobility with doping density in p+‐GaAs has been measured with the zero‐field time‐of‐flight technique. The results from a series of nine GaAs films doped between 1×1018 and 8×1019 cm−3 show the mobility decreasing from 1950 cm2 V−1 s−1 at 1×1018 cm−3 to 1370 cm2 V−1 s−1 at 9×1018 cm−3. For the doping range 9×1018–8×1019 cm−3, the decreasing trend in mobility is reversed. The measured mobility of 3710 cm2 V−1 s−1 at 8×1019 cm−3 is about three times higher than the measured value at 9×1018 cm−3. These results confirm and extend recent transistor‐based measurements and are in accord with recent theoretical predictions that attribute the increase in minority electron mobility in p+‐GaAs to reductions in plasmon and carrier‐carrier scattering at high hole densities.

Substrate temperature measurement by absorption-edge spectroscopy during molecular beam epitaxy of narrow-band gap semiconductor films

A novel method is described for utilization of absorption-edge spectroscopy (ABES) to monitor the temperature of a semiconducting substrate during molecular beam epitaxy (MBE) of a film with a band gap narrower than that of the substrate. Conventional ABES cannot be used for substrate temperature determination with narrow-band gap epilayers that are sufficiently thick so as to be opaque in the wavelength range corresponding to the substrate band gap. However, we show that by inserting a reflecting layer (or layers) between the substrate and overlying narrow-band gap epilayer, ABES temperature measurements can be carried out in reflection from the backside of the substrate, even in the presence of arbitrarily thick narrow-band gap epilayers. This approach is demonstrated for MBE growth of InAs on GaAs substrates and also for HgCdTe on CdZnTe substrates, and is shown to be accurate to ±2 °C over temperature spans of 300 and 120 °C, respectively, for these two material systems in the vicinity of the typical ...

Doping concentration dependence of radiance and optical modulation bandwidth in carbon‐doped Ga0.51In0.49P/GaAs light‐emitting diodes grown by gas source molecular beam epitaxy

Double‐heterostructure light‐emitting diodes (LEDs) consisting of an n‐Ga0.51In0.49P emitter, a carbon‐doped p‐GaAs active layer, and a p‐Al0.30Ga0.70As cladding layer have been grown by gas source molecular beam epitaxy with halomethane carbon doping sources. CCl4 and CHCl3 have been used to vary the active layer C doping level from 1018 to 1020 cm−3. Measurements of LED optical modulation bandwidth indicate that the bandwidth increases with C doping, attaining a record value of 1.6 GHz at 1020 cm−3 C concentration. The LED radiance is observed to decline significantly in the 1019–1020 cm−3 range.

Molecular beam epitaxial growth of HgCdTe midwave infrared multispectral detectors

Molecular beam epitaxy (MBE) has been utilized to fabricate high performance HgCdTe infrared detectors with sensitivity to midwave infrared radiation in adjacent spectral bands for two-color thermal imaging applications. Growth of a multilayer HgCdTe device structure by MBE enables the use of an n-p-n device architecture that facilitates pixel-level registration of images in two separate spectral bands. Device structures were grown on CdZnTe(211)(B) substrates using CdTe, Te, and Hg sources with in situ In and As doping. The composition of the HgCdTe alloy layers was adjusted to achieve detection of infrared radiation in adjacent spectral bands in the 3.5–4.5 μm wavelength range. As-grown device structures were characterized with x-ray diffraction, wet chemical defect etching, and secondary ion mass spectrometry. Mesa type devices were patterned using reactive ion etching and ohmic contacts were made to the two n-type layers for operation of the detectors in a sequential detection mode. The spectral respo...

Valence‐band‐edge shift due to doping in p+ GaAs

Accurate knowledge of the shifts in valence‐ and conduction‐band edges due to heavy doping effects is crucial in modeling GaAs device structures that utilize heavily doped layers. X‐ray photoemission spectroscopy was used to deduce the shift in the valence‐band‐edge induced by carbon (p type) doping to a carrier density of 1×1020 cm−3 based on a determination of the bulk binding energy of the Ga and As core levels in this material. Analysis of the data indicates that the shift of the valence‐band maximum into the gap and the penetration of the Fermi level into the valence bands exactly compensate at this degenerate carrier concentration, to give ΔEv =0.12±0.05 eV.

Comparative study of minority electron properties in p+-GaAs doped with beryllium and carbon

Minority electron properties in p+‐GaAs doped with beryllium (Be) and with carbon (C) are reported. Measurements of essentially identical responses for structures differing only in dopant element demonstrate that the diffusivity (Dn) and the diffusion lengths (Ln) are the same in p+‐GaAs doped to ∼1019 cm−3 with Be‐ and C‐dopants. Zero‐field time‐of‐flight analysis yields Dn=35 cm2/s and internal quantum efficiency analysis yields Ln=2.4 μm, which implies a lifetime that is approximately at the estimated radiative limit. In addition, the majority Hall mobility was also found to be identical for the Be‐ and C‐doped material.