A Transmission Electron Microscopy (TEM), Photoluminescence (PL) and Photoluminescence Excitation Spectroscopy (PLE) investigation has been conducted on Ga0 52In0.48P epilayers, grown on GaAs(001) by Gas-Source Molecular Beam Epitaxy. Selected area diffraction in the TEM shows that epilayers grown at temperatures between 480°C and 535°C exhibit CuPt-type ordering with the antiphase domain size increasing with increasing growth temperature. PLE data shows that, in the temperature range 480°C to 535°C the band gap energy of Ga0.52In0-48P epilayers increases with increasing growth temperature from 1.971 to 2.003 (±0.001 eV). For high band gap optical data storage applications these values compare well with the highest band gap energies reported for epilayers grown by MOCVD.

Fabry Perot 1550 nm sources are required for a number of high volume short haul applications, and an optimised device design is sought which is suitable for wide temperature range operation. Strain compensated multiquantum well lasers with between five and 11 wells were produced using MOCVD with ~1%, compressive strain in the wells, and ~1% tensile strain in the barriers. Electrical, optical, X-ray and TEM studies were used to determine the material properties. Although RT-PL measurements indicated good material quality for all wafers, significant degradation in device properties was observed for larger well numbers. TEM studies are presented which show the degradation to be due to the onset of “wavy layer” growth, which is also responsible for a broadening of the satellite peaks in the X-ray rocking curves for the material. Although wavy layer effects constrain the matrix, high quality devices were produced with low thresholds, high output powers, and wide temperature range operation

A Transmission Electron Microscopy (TEM), Photoluminescence (PL) and Photoluminescence Excitation Spectroscopy (PLE) investigation has been conducted on Ga 0.52 In 0.48 P epilayers grown on (001) GaAs substrates by Gas-Source Molecular Beam Epitaxy.For Ga 0.52 In 0.48 P epilayers grown on exact (001) GaAs substrates, increasing the growth temperature from 480°C to 535°C increased the antiphase domain plate thickness, t, from 7.3±0.4 to 17.4±0.9 Å, and decreased the long range order parameter, n, from 0.32 to 0.18±0.1. For epilayers grown at 530°C, on GaAs(001) substrates off-cut 0°, 7°, 10° and 15° towards [111]A, increasing the substrate misorientation from 0° to 15° decreased the antiphase domain plate thickness, from 12.3±0.6 to 6.0±0.3 Å. The long range order parameter also decreased from 0.19 to 0.10±0.01. The band gap energies of these samples, grown by GS-MBE, were close to those reported for fully disordered Ga 0.52 In 0.48 P epilayers grown by MOCVD at ∼760°C. This shows that GSMBE is also a good technique to grow GaInP for high band gap optical data storage applications and at lower growth temperatures. The optimum growth conditions in this study were at a growth temperature of 530°C on (001) GaAs substrate with 15° off-cut towards [111]A.

Transmission electron microscopy (TEM) has been used to investigate the mechanisms of misfit strain relaxation in InxGa1−xAs epilayers grown on GaAs(111¯)B substrates misoriented 2° towards [211¯]. It was found that the relaxation was brought about by a triangular network of misfit dislocations lying along the three 〈11̄0〉 directions near the interface. However, the dislocation distribution was anisotropic with a much higher density of dislocations lying parallel to the [01̄1] direction. A second relaxation mechanism was also observed which involved the formation of deformation twins. These had nucleated at the epilayer surface and grown down into the epilayer, sometimes entering the underlying buffer layer. Twin formation was also anisotropic with twins forming on the (1̄11)[211] system only. The dislocation and twin anisotropy may not be explained using the Schmid Factor considerations but is thought to be associated with heterogeneous nucleation of dislocations at the [01̄1] surface steps caused by the misorientation. The critical layer thickness for the observation of misfit dislocations by TEM in In0.25Ga0.75As (111¯)B epilayers was found to be between 15 and 25 nm. This is the same range as that observed for (001) epilayers of the same composition. This is as expected from theoretical considerations of the effects of orientation on the elastic modulus and the strain relieving component of the misfit dislocation Burgers vector.

The effects of annealing on the distribution of elements in a Au(400 nm)/Ti(75 nm)/Pd(75 nm) Ohmic contact structure on zinc-doped p-GaAs epilayers, have been investigated using secondary ion mass spectrometry and cross-sectional transmission electron microscopy. The structure remained layered upon heat treatment up to 380°C in spite of considerable elemental mixing and the formation of new phases. The metallisation/semiconductor interfacial region was found to be very reactive. At room temperature, interaction between the contact and the GaAs resulted in the formation of a 20 nm thick Pd–Ga–As ternary layer (phase I) adjacent to the substrate. Annealing the structure at temperatures of 200 and 260°C led to further interaction at the contact/GaAs boundary and to the creation of protrusions, composed of a second Pd–Ga–As ternary compound (phase II), extending 90 nm into the semiconductor substrate. Heat treatments at 320 and 380°C resulted in a uniform multi-phase layer without protrusions, of total thickness 170 nm, next to the GaAs substrate.

The ternary III-V semiconductor Ga0.52In0.48P grown on GaAs substrate has been studied for visible wavelength light sources for information processing, laser printing and compact disk systems. In epilayers grown by MOCVD or Solid Source MBE, optical emission with reduced energy is known to originate from atomic ordering of the alloy and the degree of ordering of the group III elements has been found to be significantly influenced by the degree of substrate misorientation from (001). This paper reports a Transmission Electron Microscopy (TEM) study conducted on Ga0.52In0.48P epilayers grown on misoriented (001) GaAs substrates by Gas-Source Molecular Beam Epitaxy. For a growth temperature of 530 degrees C, substrate off-cut angles of 0 degrees, 7 degrees, 10 degrees and 15 degrees towards [111]A were investigated. Selected Area Diffraction Patterns obtained, indicated that the antiphase domain size decreases with increasing off-cut. TEM results have been correlated with band gap measurements obtained from PL and PLE spectra. The band gaps of Ga(0.52)ln(0.48)P epilayers grown by GS-MBE were found to be larger than those of the same composition grown by MOCVD or Solid Source MBE. This indicates potential for laser devices of shorter wavelengths.

A Transmission Electron Microscopy (TEM), Photoluminescence (PL) and Photoluminescence Excitation Spectroscopy (PLE) investigation has been conducted on Ga0.52In0.48P epilayers, grown on GaAs(001) by Gas-Source Molecular Beam Epitaxy. Selected area diffraction in the TEM shows that epilayers grown at temperatures between 480 degrees C and 535 degrees C exhibit CuPt-type ordering with the antiphase domain size increasing with increasing growth temperature. PLE data shows that, in the temperature range 480 degrees C to 535 degrees C the band gap energy of Ga0.52In0.48P epilayers increases with increasing growth temperature fi om 1.971 to 2.003 (+/-0.001 eV). For high band gap optical data storage applications these values compare well with the highest band gap energies reported for epilayers grown by MOCVD.

Growth of highly (111) oriented, highly coalesced diamond films on platinum (111) surface-A possibility of heteroepitaxy

HREM studies of c-axis oriented GBCO films, with Tc > 90 K and Jc > 106 A/cm2 at 77 K, have shown that they contained two dense distributions of particles, one coarse and one fine. The coarse particles were found to be composed of agglomerates of very fine a-axis oriented grains, having c-axes in two perpendicular directions, together with other second phases. The fine particles were isolated a-axis oriented grains, some of which formed a ‘sandwich’ with Gd2O3 at the centre. Anti-phase boundaries were frequently observed in the film and grain boundaries with an angle of 45° were occasionally observed.

The microstructure and electrical properties of as deposited and annealed Au (400 nm)/Pd (75 nm)/Ti (10 nm) contact structures to p type GaAs, C doped with a concentration of 5 x 10(18) and 5 x 10(19) cm(-3), have been investigated using transmission electron microscopy, and current-voltage measurements as a function of temperature in the range 198-348 K. The specific contact resistivities have also been measured using the transmission line method. It was found that increasing the epilayer doping level by an order of magnitude, from 5 x 10(18) to 5 x 10(19) cm(-3), caused the dominant current transport mechanism to change from thermionic field emission to field emission. For the lower level doped epilayers generation-recombination within the depletion region was found to be the dominant current transport mechanism for temperatures below 298 K. The contacts to the more highly doped epilayers (C doped, 5 x 10(19) cm(-3)) had specific contact resistivities of 0.08 +/- 0.03 Ohm mm and 0.05 +/- 0.06 Ohm mm, respectively. These values, together with a minimal metal penetration in the semiconductor of <15 nm, indicate that these contacts are suitable for heterojunction bipolar device applications.

Si1-xGex/Si MODFET structures, incorporating Si1-xGex graded buffer layers, (x = .05 to .35), have been grown by Gas-Source Molecular Beam Epitaxy on (001) substrates. Relaxation of the buffer layers and the influence of the graded buffer layer growth temperature have been studied by TEM and EBIC-SEM. The majority of the misfit dislocations were confined within graded buffer layers and were of 60 degrees type. Structures having graded buffer layers grown at 615 degrees C showed undulation of the device layers and threading dislocation densities of up to 2 x 10(7) cm(-2). However, lower buffer layer growth temperatures of 565 degrees C or 515 degrees C produced structures with more planar device layers and threading dislocation densities less than or equal to 4 x 10(6) cm(-2), showing potential for MODFET device applications.

The Ge thickness, x, of NiAuGe(5 nm/45 nm Ix nm)/ZrB2(50 nm)/Au(20 nm) ohmic contacts to n-InGaAs was varied between 0 and 20 nm. The microstructures of these contacts, after annealing at 270-degrees-C, were investigated using transmission electron microscopy (TEM) and correlated with the respective specific contact resistances. In the absence of Ge, a Ni-Ga-As phase was formed at the metal-semiconductor interface and the specific contact resistance was high (0.63 OMEGA mm). When thicknesses of x = 1 0 nm or x = 15 nm of Ge were added, Ni-Ge-As phases were observed, but they were replaced by AuGeAs and NiGe when x = 20 nm. The specific contact resistance was a minimum (0.11 OMEGA mm) for this composition. Ge was clearly beneficial for ohmic-contact formation. The low-temperature I-V characteristics of the contact containing the largest amount of Ge (that is, x = 20 nm) indicated that electron tunnelling through degenerately-Ge-doped regions was not the dominant ohmic mechanism in these contacts.

The Ge thickness, x, of NiAuGe(5 nm/45 nm/xnm)/ZrB2(50 nm)/Au(20 nm) ohmic contacts to n-lnGaAs was varied between 0 and 20 nm. The microstructures of these contacts, after annealing at 270°C, were investigated using transmission electron microscopy (TEM) and correlated with the respective specific contact resistances. In the absence of Ge, a Ni-Ga-As phase was formed at the metal-semiconductor interface and the specific contact resistance was high (0.63 Ωmm). When thicknesses of x = 10 nm or x = 15 nm of Ge were added, Ni-Ge-As phases were observed, but they were replaced by AuGeAs and NiGe when x = 20 nm. The specific contact resistance was a minimum (0.11 Ωmm) for this composition. Ge was clearly beneficial for ohmic-contact formation. The low-temperature I–V characteristics of the contact containing the largest amount of Ge (that is, x = 20 nm) indicated that electron tunnelling through degenerately-Ge-doped regions was not the dominant ohmic mechanism in these contacts.

AuGeNi/ZrB2/Au ohmic contacts annealed at 270-degrees-C or 445-degrees-C were investigated using TEM. Reaction of the 270-degrees-C annealed sample took place via solid state diffusion resulting in the formation of AuGeAs and NiGe interfacial phases. In the sample alloyed at 445-degrees-C, melting of the contact resulted in a more extensive reaction. The morphology as well as the contact resistivity (0.47-OMEGA-mm) was inferior. The phases formed were Au-In compounds, f.c.c. Ni-Ge-As and regrown InxGa1-xAs (x < 0.3).

A series of layers of InAs has been grown on GaAs (001) by MBE with a wide range of growth conditions. Cross-sectional TEM studies showed the presence of (InGa)As protrusions into the GaAs at the interface in all samples. The formation of these protrusions is thought to be due to the presence of In droplets which react with the GaAs at the early stage of InAs deposition.

A secondary ion mass spectrometry (SIMS) investigation has been carried out on alloyed, Pt/Zn/Pt/ZrB2/Au, ohmic contacts to p-InGaAs, on InP(001) substrates, in order to determine metal penetration depths into the semiconductor. The resolution obtained using front-surface and back-surface SIMS profiling has been compared. It has been demonstrated that front-surface profiles suffer reduced resolution as a result of surface roughness and sputter-induced roughening by the ion beam. Improved-resolution, back-surface SIMS profiles, supported by transmission electron microscopy, show negligible penetration of Au, Pt or Zn into the InGaAs, within the limits of obtainable depth resolution. However, some P diffusion from the InP into the InGaAs is indicated.

Au/Pd/Ti and Au/Ti/Pd ohmic structures to thin p+-GaAs layers have been investigated for use as contacts to the base region of HJBTs. The Au/Pd/Ti contact system yielded specific contact resistivities at or above 2.8 × 10-5Ωcm2. Heat treatments up to 8 minutes at 380°C caused only limited interaction between the metallization and the semiconductor. The metal penetrated to a maximum depth of ≃2nm. Specific contact resistivity values less than 10-5Ω2 were achieved using the Au/Ti/Pd (400/75/75nm) scheme. The nonalloyed Au/Ti/Pd contact showed the best combination of electrical and structural properties with a contact resistivity value of 9 × 10-6Ωcm2 and Pd penetration of the GaAs epilayer to a depth of ≃30nm.

The microstructure and contact resistance of NiAuGe contacts to n-type GaAs were determined as a function of initial contact composition. The contact microstructures were found to contain varying amounts of of α, α’ and β (or Au7Ga2) Au-Ga, epitaxial Ge, NiGe and NiGeAs phases. A previously unidentified NiAsx (Zr,B) phase was also observed. The contact resistance was found to vary between 0.22–0.38±0.03Ωmm. Comparison of the microstructural and contact resistance data revealed that the ohmic formation models based on (i) the formation of a recrystallised n+ GaAs layer and (ii) the presence of a graded Ge/GaAs heterojunction were not applicable to this contact system.