James S.C. Chang

Composition non-uniformities in selective area growth of GaInAs on InP grown by OMVPE

Selective area epitaxial growth of Ga0.47In0.53As on InP substrates patterned with silicon nitride was done by low pressure organometallic vapor phase epitaxy. Good surface morphology and clean side walls of the epitaxial layers were obtained in most of the areas of selective GalnAs growth. However, both GaAs incorporation and InAs incorporation increased near the edges of the selective growth areas due to the extra flux of Gacontaining and In-containing species migrating on the surface of silicon nitride. The increase in InAs incorporation was found at a higher rate when the adjacent silicon nitride area was large, hence, cross-hatching appeared near the edges. A characteristic length of adjacent silicon nitride seemed to be connected with the enhanced InAs incorporation, which was about 40μm at 600°. The non-uniformities in composition appeared in all wafers grown in the temperature range between 570 and 650°.

Franz–Keldysh oscillations from combined space-charge and grading fields as observed in graded emitter GaAlAs/GaAs heterojunction bipolar transistor structures

We have performed a systematic room-temperature photoreflectance study of Franz–Keldysh oscillations from the Ga0.77Al0.23As emitter and GaAs collector regions of a series of graded band-gap emitter GaAlAs/GaAs heterojunction bipolar transistor structures in which both the emitter grading and doping [space-charge field (SCF)] have been varied. It is found that the fields in the emitter depend on both the grading field and SCF, in agreement with the recent theory of Sun and Pollak [W. P. Sun and F. H. Pollak, J. Appl. Phys. 83, 4447 (1998)]. Good agreement for both the collector and emitter fields is found between experiment and simulation using a comprehensive, self-consistent model, including the photovoltaic effect.

Dislocation gettering in semi-insulating GaAs investigated by cathodoluminescence

The cathodoluminescence (CL) imaging technique is applied to the characterization of semi‐insulating GaAs substrates after an extrinsic gettering treatment. A reverse contrast CL image is found for the gettered material. This study provides evidence for the physical mechanism taking place in the gettering process and contributes to the understanding of the effect of dislocations on device performance.

Leakage current in GaInAs/InP photodiodes grown by OMVPE

Reverse-bias dark current and zero-bias dynamic conductance are studied for large area p-i-n photodiodes of Ga0.47In0.53As grown on InP substrates by organometallic vapor phase epitaxy (OMVPE). The leakage in GaInAs homojunction mesa diodes is dominated by generation current near the intersection of the mesa surface with the GaInAs depletion region. The dynamic conductance at zero volts depends on both the length and orientation of the perimeter for these diodes. Double heterostructure InP/GaInAs/InP photodiodes with the p-n junction in the InP demonstrate lower zero-bias conductance which depends on diode area. The temperature dependence of leakage current in a double heterostructure p-i-n diode on a p-substrate is approximately fit by generation current in the GaInAs as well but with a much larger effective generation lifetime. The lowest leakage current measured is J = 3.6 × 10-7 A/cm2 at - 10 V for this structure. Responsivities of these diodes at 1300 nm are 0.9 A/W for reverse biases 6 V. Using InP regrowth, 600 μm diodes with 300 K dynamic conductance < 7 × 10-7 Ω-1 and responsivity 0.95 A/W at 0 V are fabricated.

Effect of crystalline defects on electrical properties of heavily Si‐doped strain‐relaxed In0.5Ga0.5As layers grown by molecular beam epitaxy on GaAs

Heavily Si‐doped, strain‐relaxed In0.5Ga0.5As layers are often used as contact layers on N+ GaAs to form nonalloyed ohmic contacts. The present work studies the electrical properties of such In0.5Ga0.5As layers grown on undoped GaAs buffer layers by molecular beam epitaxy both as‐grown and after anneals at temperatures between 300 and 430 °C. It is found that in the as‐grown condition, there is a region of about 150 A extending into the In0.5Ga0.5As layer contiguous to the In0.5Ga0.5As/GaAs interface where both the electron concentration and mobility decrease toward the interface. With postgrowth anneal, the electron concentration in this region will be further reduced and the width of the region will be increased. The associated activation energy is estimated to be 0.99±0.41 eV. This phenomenon can be fully explained in terms of defect structural changes during anneal. This work provides strong evidence to indicate that the as‐grown In0.5Ga0.5As layers are not in thermodynamic equilibrium and will continue to relax when thermal energy is provided.