P. Kightley

Characterization of epitaxial and oxidation‐induced stacking faults in silicon: The influence of transition‐metal contamination

Photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), and defect etching have been used to characterize epitaxial stacking faults (ESF) in silicon epilayers grown by low‐pressure chemical vapor deposition (LPCVD) and oxidation‐induced stacking faults (OISF) in high‐purity float‐zone (FZ) Si. No dislocation‐related luminescence was observed from either ESFs or OISFs grown under clean conditions. Deliberate surface contamination, followed by annealing with Cu, Fe, Ni, Ag, or Au in the range 4×1012–2×1016 atoms cm−2 introduced dislocation luminescence features, with a maximum intensity at ≊4×1012 atoms cm−2. TEM examination revealed that there was no evidence for precipitation at low levels of contamination but as the contamination level increased metal‐related precipitates were observed on the bounding partial dislocations.

Dynamic optical reflectivity to monitor the real‐time metalorganic molecular beam epitaxial growth of AlGaAs layers

Oscillations in the reflectivity of AlxGa1−xAs, grown on GaAs at 870 K have been measured at 632.8 nm over the range 0≤x≤1. The oscillations are fitted to the standard theory of reflection from a bilayer with the complex refractive index (n+ik) of substrate and film as fitting parameters. For GaAs the values of n and k are measured as 3.9+i0.23 at 870 K. Assuming n varies linearly with x for AlxGa1−xAs between 3.1(A1As) and 3.9(GaAs) then the period of the oscillations gives an accurate measurement of growth rate, while the amplitude allows the film composition to be monitored simultaneously. All layers were grown by metalorganic molecular beam epitaxy (MOMBE).

CBE growth of GaAs/GaAs, GaAs/Si and AlGaAs/GaAs using TEG, AsH3 and amine-alane precursors

The growth of high quality AlGaAs by CBE bas been limited by the high levels of carbon and oxygen contamination. The use of alane based precursors offers a significant reduction in such contamination. We report for the first time the CBE growth of AlxGa1-xAs from triethylgallium, dimethylethylamine-alane and arsine, and compare with. growth from triethylgallium, trimethylamine-alane and arsine. Some preliminary results of work on the CBE growth of GaAs on silicon will also be reported.

Metal‐induced dislocation nucleation for metastable SiGe/Si

A new mechanism of misfit dislocation nucleation is demonstrated. Deliberate contamination with approximately 0.003 monolayers of Cu and subsequent annealing at 600 °C is shown by transmission electron microscopy, photoluminescence, and defect etching to produce dislocation half loops in a 1.1 μm layer of Si0.93Ge0.07 on a silicon substrate.

A mechanism of misfit dislocation reaction for GaInAs strained layers grown onto off-axis GaAs substrates

The structure of misfit dislocations at the interface between compressively strained epitaxial In0.12Ga0.88As and GaAs has been studied by TEM. Two dislocation line directions, separated by ∼2° in both the nominal [110] and [110] directions, are observed for growth on (001) substrates tilted ∼2° off toward (010). Only [110] and [110] glide directions are observed for growth on nominally on-axis substrates. It is shown that the misfit dislocations are constrained to lie in the interface plane often generating long segments of edge dislocation where the misfit dislocations are forced to converge by the low angle offset. The edge segments curve out of the interface plane into the buffer layer.

Monitoring real-time CBE growth of GaAs and AlGaAs using dynamic optical reflectivity

Abstract Dynamic optical reflectivity (DOR) uses the interference oscillations arising from the multiple reflections, of a normally incident CW laser beam, between the surface of a growing film and the film-substrate interface. The oscillations have a period determined by the refractive index of the film and the laser wavelength. DOR measurements have been made, in real time, during the CBE growth of Al x Ga 1− x As layers on a GaAs(100) substrate. The results show that the growth rate and the aluminum composition x can be monitored.

Growth of strained InAs/InP quantum wells by molecular beam epitaxy

InAs/InP compressively strained quantum well structures with well thicknesses (LZ) 5 to 53 A have been grown by solid source molecular beam epitaxy. Relatively sharp, intense, photoluminescence (PL) is observed over the wavelength range 1.1–2.05 μm at 10 K, with linewidths as narrow as 14 meV for a 30 A well. Quantum confinement results in a shift of PL peak position of 130–710 meV with respect to the band gap of bulk strained InAs. The shifts are consistent with a conduction band offset (ΔEc) of 40%. At 300 K the wavelength range is extended to 2.23 μm, a value which to our knowledge is the longest wavelength reported for InAs/InP quantum wells. The high quality of pseudomorphic structures with well thicknesses exceeding estimates of critical layer thickness is demonstrated by transmission electron microscopy studies.

Effect of misfit dislocations on leakage currents in strained multiquantum well structures

The reverse leakage current in strained multiple quantum well (MQW) p‐i‐n structures has been measured for a range of different dimensions and strain. The magnitude of the leakage current is found to be dependent on the average strain of the MQW, the total MQW thickness and the thickness of the capping layer. Plan view transmission electron microscopy shows that misfit dislocation arrays form primarily at the upper and lower MQW interfaces and the total density of these determine the leakage current.

XeCl excimer laser assisted CBE growth of GaAs

Abstract The effect of 12 ns, 308 nm (XeCl) excimer laser pulses on the CBE growth rate of GaAs, at temperatures below the maximum non-laser assisted growth rate, G max , has been studied as a function of laser fluence and repetition frequency. There is a threshold fluence for growth rate enhancement, above which the growth rate is dependent on repetition frequency, being restored to G max at 20 Hz. The growth rate in the laser spot is measured by dynamic optical reflectivity (DOR).

The Generation and Optical Activity of Misfit Dislocations by Very Low Level Transition Metal Contamination of SiGe/Si.

An initially pseudomorphic Sio.93Geo.07 layer is forced to relax after the deposition of 0.003 monolayers of Cu contamination and a 600°C anneal. Photoluminescence shows the dislocations have similar luminescence features (D1 to D4) to dislocations generated in bulk silicon. TEM is used to study the generation of the misfit dislocations. It is shown that the half loops form at the sample surface and a mechanism that involves the action of both the metal contaminant and the surface steps is suggested to explain the geometric arrangement of the dislocation loops that are present. The sample was found to be only 22% relaxed whereas equilibrium theory predicts 92% relaxation.