A. Taike

p‐type conductivity control of ZnSe highly doped with nitrogen by metalorganic molecular beam epitaxy

p‐type ZnSe with resistivity low enough for device application has been realized by metalorganic molecular beam epitaxy. This method has enabled growth of p‐type ZnSe doped with nitrogen at concentrations as high as 1019 cm−3 by using ammonia as a dopant source. The dependence of photoluminescence and electrical properties on substrate temperature has been investigated. Hall measurements show p‐type conductivity with a resistivity of 0.57 Ω cm, a carrier concentration of 5.6×1017  cm−3, and a Hall mobility of 20 cm2/V s.

ZnSe p‐n junctions produced by metalorganic molecular‐beam epitaxy

The p‐n junction in nitrogen‐doped p‐type ZnSe/undoped n‐type ZnSe on n‐type GaAs (100) is successfully produced by metalorganic molecular‐beam epitaxy. p‐type conduction of ZnSe is achieved as a consequence of high nitrogen doping (5×1018–1×1019 cm−3). The data points of C−2 (C: capacitance) against voltage of the p‐n junction are approximated by a straight line and the diffusion potential estimated from the plots is about 2.4 eV. Electron‐beam‐induced current also directly demonstrates the formation of a ZnSe p–n junction. Furthermore, blue emission is observed from the 5‐V foward‐biased ZnSe p‐n junction at 77 K.

p-Type conduction of ZnSe highly doped with nitrogen by metalorganic molecular beam epitaxy

Abstract Highly conductive p-type ZnSe layers have been grown reproducibly as a consequence of high nitrogen-doping (≈1019cm-3) by using metalorganic molecular beam epitaxy (MOMBE). The dependence of electrical and photoluminescent properties on substrate temperature (Ts) has been investigated. p-Type conductivity of the ZnSe films at room temperature is enhanced with an increase in Ts; e.g. from a high 0.1 MΩcm resistivity at Ts=300°C to a low 0.57 Ωcm resistivity at 450 °C. By contrast, the dependence of the electrical properties for undoped ZnSe on Ts is similar to that of nitrogen-doped ZnSe except for the type of conductivity. The n-type resistivity of undoped ZnSe also decreases with an increase in Ts (e.g. 20 KΩcm at 300°C to 3.5 Ωcm at 400°C). A nitrogen-doped p-type ZnSe/undoped n-type ZnSe junction grown at 350°C on n-GaAs (100) has been succesfully produced. The diffusion potential of the p-n junction can be evaluated to be between 2.45 and 2.55 eV from the C-2-V plot. Observations of electron beam induced current (EBIC) have also shown formation of the p-n junction. At 77 K bluish emission has been observed from the p-n junction with a 5V forward-bias voltage.

Large number of periods in highly strained InGaAlAs/InGaAlAs MQW structures grown by metalorganic vapor-phase epitaxy

We have found that the crystalline quality at the well-barrier interfaces of an InGaAlAs strain-compensated MQW structure grown by MOVPE is much higher than that of an InGaAsP strain-compensated MQW structure, especially for a high strain. A large number of periods (25) in a highly strained (+1.4%) InGaAlAs MQW structure was obtained while preserving high crystalline quality by using the InGaAlAs strain-compensated structure.

Crystallographic microstructure and electrical characteristics of Au/Pt/Ti/Ni ohmic contacts on p‐type (001) ZnTe layers

The crystallographic microstructure and electrical characteristics of Au/Pt/Ti/Ni ohmic contacts on p‐type (001) ZnTe layers are investigated as a function of annealing temperature, by using the transmission line model method, cross‐sectional transmission electron microscopy, and Auger electron spectroscopy. The specific contact resistance decreases when the annealing temperature is increased and reaches a minimum at 300 °C. A minimum value of 1.1×10−6 Ω cm2 is obtained for a hole concentration of 3×1019 cm−3. The epitaxial NiTe2 that formed at the metal/semiconductor interface due to annealing is considered to play an important role in lowering the contact resistance. The excess Zn atoms created by the reaction between Ni and ZnTe are found to diffuse upward and to segregate at the Pt/Ni interface. A contact stability test performed at 102 °C suggests that these ohmic contact structures are stable even under high‐current injection.

Electrical properties and microstructures of Au/Pt/Ti/Ni ohmic contacts to p‐type ZnTe

Electrical properties and microstructures of Au/Pt/Ti/Ni ohmic contacts to p‐type ZnTe were investigated using the transmission line model method and cross‐sectional transmission electron microscopy. The specific contact resistance decreases when the annealing temperature is increased and reaches a minimum at 300 °C. The formation of NiTe2 from the reaction between Ni and ZnTe plays an important role in lowering the contact resistance. A contact stability test performed at 102 °C suggests that these ohmic contacts are stable even under high‐current injection.

DISORDERING OF THE ZNCDSE SINGLE QUANTUM WELL STRUCTURE BY CD DIFFUSION

The effects of annealing on a ZnCdSe single quantum well (SQW) structure with ZnCdSSe/ZnSSe superlattice optical guiding layers are investigated. X‐ray diffraction and photoluminescence (PL) measurements showed disordering of a ZnCdSSe/ZnSSe superlattice after annealing at about 500 °C. The PL peak energy of the SQW shifted to the higher energy side, and the linewidth narrowed in the sample annealed at 300 °C. Cadmium diffusion was confirmed by secondary ion mass spectrometry. We found that the disordering of the ZnCdSSe/ZnSSe superlattice and the changes in the emissions from the SQW were due to the Cd diffusion.

Reliable wide-temperature-range operation of 1.3-/spl mu/m beam-expander integrated laser diode for passively aligned optical modules

A novel structure for a 1.3-/spl mu/m beam-expander integrated (BEX) laser diode is demonstrated. It combines a thickness-tapered InGaAsP-InP multiple quantum-well (QW) crystal grown by a novel silicon shadow masked metalorganic vapor phase epitaxy and a simple reverse-trapezoid-ridge waveguide laser structure that offers smooth mode field expansion and improved high-temperature lasing performance. We found this new BEX laser quite suitable for operation over a wide range of temperatures above 85/spl deg/C and highly efficient lens-free coupling to a single-mode fiber (SMF) of less than 3 dB. These excellent lasing properties along with reliability under severe environmental conditions make this BEX-LD a promising candidate for practical use for low-cost long-wavelength light-source modules using optical passive alignment techniques.

Effect of N-doped ZnTe layers on ZnSeZnTe graded superlattices

Abstract The effect of the nitrogen concentration on the properties of ZnTe-based contact structures consisting of a p-ZnTe layer, a ZnSe ZnTe graded superlattice (SL), and a p-ZnSe layer is described. The degree of nitrogen-doping into the ZnSe ZnTe SL and into the ZnTe layer was changed by modulation doping. The ohmic I-V characteristics were observed in samples with an N-doped ZnSe undoped ZnTe SL and in samples with a ZnTe layer with a nitrogen concentration of 3 × 1018cm−3. When the nitrogen concentration in the ZnSe ZnTe SL region or the ZnTe layer was increased, nitrogen diffusion into the ZnSe layer was observed by SIMS and PL measurement. The ZnSe layer then became highly resistive, probably because deep donors were induced by the nitrogen diffusion.

Dependence of ZnTe‐based contact structure properties on nitrogen concentration

The effect of nitrogen concentration on the properties of ZnTe‐based contact structures, which consist of p‐ZnTe layers, ZnSe/ZnTe graded superlattices and p‐ZnSe layers is described. The nitrogen concentration of the ZnTe layer was varied by using a modulation doping method. Ohmic I–V characteristics were observed when the nitrogen concentration of the ZnTe layer was as low as 3×1018 cm−3. When the nitrogen concentration rose above 1×1019 cm−3, however, no current was observed in the I–V curves. Nitrogen diffusion from the ZnTe layer to the superlattice and the ZnSe layer was observed by SIMS analysis and PL measurement. The ZnSe layers became highly resistive, probably because deep donors were induced by the nitrogen diffusion.