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Cross-sectional scanning tunneling microscopy (STM) has been used to study in-operation changes that occur at the active region of clean-cleaved semiconductor laser diodes. A tunneling model that allows the inclusion of tip-induced band bending and surface defect states has been used to study the origin of the surface changes which give rise to the observed modification. Low-doped layers close to the active region are found to undergo both a reduction in doping concentration and an increase in the surface defect state density as the lasers are operated. These changes ultimately lead to device failure. Under different tunneling modes STM can be sensitive to one effect or the other, and the importance of modeling the changes to confirm which are occurring is emphasized. [ABSTRACT FROM AUTHOR]

The formation of the Ni/Al0.2Ga0.8N Schottky contacts has been investigated by x-ray photoelectron spectroscopy. In situ scanning tunneling microscopy was used in parallel to investigate the morphology of the Ni covered surface after the last deposition. In the same way, results are presented through two perspectives: the intensity of core-level signals which give information on the growth mode, and the core-level binding energy positions which assess changes in electronic and chemical properties as a function of Ni coverage. Ni deposition on Al0.2Ga0.8N substrates follows the Stranski–Krastanov growth mode. It is suggested that Ni preferably reacts with the contaminants at the surface rather than with the epilayer itself. The Schottky barrier formation is discussed in terms of unified defect and metal-induced gap states models. [ABSTRACT FROM AUTHOR]

Cross-sectional scanning tunneling microscopy is applied to semiconductor lasers which are biased and producing light. Two device structures are investigated—a double quantum well laser and a buried heterostructure device with two-dimensional growth variation. Scanning tunneling microscopy (STM) images are collected as a function of sample drive bias. Changes that occur in the STM image as a result of powering the sample are observed, which are due to changes in the energy band structure and the carrier concentration in the device as it responds to bias. The observed changes are largely reversible and a model is presented which matches and confirms this behavior. Once these effects are confirmed and decoupled, the technique can be used to study device-specific behavior resulting from physical changes in lasers as they are operated. [ABSTRACT FROM AUTHOR]

Severe electron leakage impedes the full exploitation of AlGaInP laser diodes in the 630 nm regime. Such thermally activated currents are attributed to inherently small conduction band offsets and intervalley transfer between the Γ and X conduction band minima. To negate the detrimental effect of these two intrinsic material issues a theoretical model is proposed. A multi-quantum-barrier (MQB) structure able to inhibit both Γ- and X-band transmissions is inserted in the p-doped region adjacent to the active region of the device, allowing a greater percentage of injected electrons to be reflected back within the active region. The design of the MQB follows a strict optimization procedure that takes into account fluctuations of superlattice layer width and composition. This model is used in conjunction with a dual conduction band drift-diffusion simulator to enable the design of the MQB at an operating voltage and hence account for nonlinear charge distribution across it. Initial results indicate strong agreement between experimentally determined effective enhancements and those predicted theoretically. [ABSTRACT FROM AUTHOR]

The adsorption of Ni on 4H-SiC surfaces as a function of temperature has been investigated using scanning tunneling microscopy (STM) and variable tip-sample separation scanning tunneling spectroscopy (VTSS-STS). A submonolayer of Ni was deposited on an atomically clean ([Square_Root]3×[Square_Root]3) 4H-SiC sample, which was then annealed sequentially from 400 to 1000 °C. VTSS-STS showed a reduction in the apparent surface band gap after Ni deposition, attributed to metal induced gap states. The size of the Ni clusters changed after annealing, due to the formation of Ni-silicides and diffusion. The surface band bending on Ni clusters increased upon annealing to 500 °C, in good agreement with Schottky contact formation models. After annealing at 1000 °C for 3 min, various surface reconstructions were observed with STM, which are typical of graphite. Ni-silicide clusters also diffused into the SiC and some could still be observed below the graphite surface. VTSS-STS measurements of the graphite surface above diffused clusters displayed Ohmic behavior. [ABSTRACT FROM AUTHOR]

Cross-sectional scanning tunneling microscopy (XSTM) is used to study a multi-quantum-barrier (MQB) structure consisting of (Al0.7Ga0.3)0.5In0.5P/(Al0.3Ga0.7)0.5In0.5P semiconductor superlattice for use in AlGaInP laser devices. Quantitative analysis of the MQB was made difficult by poor image contrast due to the intrinsic small band offset of 80 meV between adjacent layers in the large band-gap semiconductor superlattices. This is in addition to the presence of cleavage-induced monatomic steps at the clean cleaved (110) surface as they effectively mask the weak electronic features of the superlattice. To overcome these problems, the image contrast was enhanced by the choice of tunneling conditions, in particular, reducing the tip-sample separation and the origin of this mechanism is believed to be associated with tip-induced band bending. In addition, the use of arithmetic manipulation of images to eliminate physical features such as step defects on the cleaved surface is also reported. This allowed quantitative analysis to be performed on the superlattice. Results from the XSTM studies showed that the (Al0.7Ga0.3)0.5In0.5P/(Al0.3Ga0.7)0.5In0.5P superlattices have very limited interdiffusion. This is in stark contrast to other MQB candidates involving Al0.5In0.5P/Ga0.5In0.5P and Al0.5In0.5P/(Al0.3Ga0.7)0.5In0.5P superlattices which revealed extensive broadening of the well in the superlattices as previously studied by the authors. [ABSTRACT FROM AUTHOR]

Presents a study which used a scanning tunneling microscope to analyze formation of silicon overlayers deposited at room temperature. Limitation of electronic devices; Methodology; Results; Conclusions.

Deals with a study of electron sub-band occupancies and saturation effects in silicon delta-doped gallium arsenide samples, using Hall and Shubnikov-de Haas measurements in conjunction with numerical modeling. Experimental details; Results and discussion; Conclusion.

Studies the electrical and chemical properties of interfaces formed at room temperature, between the epitaxial n-type In[suby]Al[sub1-y]As(100) and a selection of metals. I-V characteristics of various metal diodes formed on clean, lattice matched In[suby]Al[sub1-y]As(100) surfaces; Aging effects for diodes formed on clean gallium arsenide surfaces; Air exposure of indium contacts.