Fanghai Zhao

Self-organized InAs quantum dots formation by As/P exchange reaction on (001) InP substrate

In this letter, we present the results of InAs quantum dots (QDs) prepared on a (001) InP substrate. As/P exchange reaction at the surface of InP buffer was used to form the InAs islands in the reactor of low pressure metalorganic chemical vapor deposition at 600 °C. Preliminary characterizations of the InAs QDs have been investigated by using atomic force microscopy and photoluminescence (PL). Room temperature PL emission from the 0-dimensional system centers at 1520 nm and the full width at half maximum of the PL is 92 meV.

Using the tensile stress field to control quantum dot arrangements

In this paper, a tensile-strained layer is used to control the quantum dot arrangements. A 3 nm GaAs tensile-strained layer is grown on InP (001) substrate, and a four-monolayer InAs compressed layer is then grown on top by LP-MOVPE. Atomic force microscopy (AFM) measurements were performed. AFM images indicate that the InAs quantum dots are arranged along two orthogonal directions, their diameter is about 30 nm, the size fluctuation is only 10%, and their density is 8.8×109 cm−2, which is higher than that grown directly on InP or GaAs substrates. An identical structure, except for the presence of 30 nm of GaAs, was also grown. The islands on top of the 30 nm GaAs are mainly very big and rectangular in shape. We demonstrate that these characteristics originate from the modulated stress field of the GaAs tensile-strained layer.

Photoluminescence of InAs Self-Organized Quantum Dots Formation on InP Substrate by MOCVD

In this letter, we present results of photoluminescence (PL) emission from single-layer and multilayer InAs self-organized quantum dots (QDs), which were grown on (001) InP substrate. The room temperature PL peak of the single-layer QDs locates at 1608 nm, and full width at half-maximum (FWHM) of the PL peak is 71 meV. The PL peak of the multilayer QDs locates at 1478 nm, PL intensity of which is stronger than that of single-layer QDs. The single-layer QD PL spectra also display excited state emission and state filling as the excitation intensity is increased. Low temperature PL spectra show a weak peak between the peaks of QDs and wetting layer (WL), which suggests the recombination between electrons in the WL and holes in the dots.

Spontaneously ordered InAs self-assembled quantum dots grown on GaAs/InP substrate

In this paper, we present a method to control the nucleation sites of InAs self-assembled quantum dots (QDs). Tensile strained material, such as GaAs used here was grown on InP substrate before InAs deposition. This thin GaAs layer can provide a surface with gridded trenches which have the same function as atomic steps and are promising for the formation of QDs with nucleation sites controlled. Atomic-force microscopy measurement was performed and the AFM images indicate that the InAs islands grown with our technique is grid aligned and have good homogeneity and low-size fluctuation. In addition, another kind of three-dimensional structure with larger size would co-exist with normal QDs if 30 nm thick GaAs layer were deposited.

Terraced substrate inner stripe visible semiconductor laser and its arrays

Lasers emitting in the range of 7500-7800 AA, which have average current thresholds of 30-40 mA and maintain single transverse mode operation up to 20 mW, are reported. Life tests show that the lasers have almost no threshold change after 3000 h of aging at 4-mW CW operation. The terraced substrate inner stripe laser arrays have clean single-lobe far-field patterns with full width at half power of 6 degrees in CW operation and 2.4 degrees in pulsed operation. >

Low resistance and large current range CW single-mode top surface-emitting laser with small window

We report the results of a room-temperature CW top surface-emitting laser whose light-emitting window is much smaller than the current injection area. The lowest series resistance of device is 50 Ω. It maintains single transverse mode at high current levels.

Trapezoidal channeled substrate inner stripe phase-locked semiconductor laser arrays

A novel type of trapezoidal channeled substrate inner stripe diode laser array grown by single‐step liquid‐phase epitaxy was designed and fabricated. A six‐element array with evanescent wave coupling, as well as leaky wave coupling, shows a continuous‐wave threshold current of 170 mA and a pulsed peak power over 675 mW per facet without a coating. A clean single‐lobe far‐field pattern of beam width 2.4° is obtained.

InP-based monolithic integration of 1.55-μm MQW laser diode and HBT driver circuit

An improved fabrication process and related experiment results of an InP-based monolithic integrated transmitter OEIC with a 1.55 micrometers MQW laser diode (LD) and an InP/InGaAs heterojunction bipolar transistors (HBT) driver circuit are presented. The epitaxial structure of the laser and driver circuits were continuously grown on semi- insulating Fe-doped InP substrate by a metal-organic chemical vapor deposition system using a vertically integration. HCL, H3PO4/H2O2 and HBr/HNO3 solution system were involved as selective or nonelective wet chemical etching respectively for the epitaxies of InP, InGaAs and InGaPAs. Both a nearly-standard contact photolithography depending on a two-step exposure technique and an electrical connection related to smoothly wet chemical etching profile of InP and InGaP in the crystal direction of (01-1) were developed in the process. The laser diode with a 3-um-wide ridge waveguide forming by a double- groove process self-aligned to the metal contact of P-type region showed an average threshold current as low as about 10mA. The HBT with a 120-nm-thick base layer performed a DC current gain of about 60-70 and an emitter-collector breakdown voltage of up to 4-5V. A clear eye diagram of the monolithic transmitter under a pulsed operation with 622Mbit/s bitrate nonreturn-to-zero pseudorandom code was obtained.

Channelled substrate window twin stripe GaAs/GaAIAs visible lasers: fabrication and steady-state analysis

GaAs/GaAIAs high-power window stripe lasers have been developed with a uniform active layer in the region adjacent to the device facets and with a curved active layer in the central region. A single-step liquid-phase epitaxy growth is used in the fabrication process to form two internal lateral current paths, so allowing for a very simple fabrication process. The optical coupling between the two stimulation emission regions reduces the beam divergence. The steady-state analysis of such a laser structure, including heating effects, agrees well with experimental results.

Novel hybrid construction of a visible surface-emitting laser and its two-dimensional arrays

A novel hybrid surface-emitting laser and two-dimensional laser array is reported. The device consists of rectangular GaAs reflectors and edge-emitting single laser or one-dimensional laser arrays which are fabricated separately. The devices are mounted upside-down on a copper heat sink, allowing for good heat conduction. The CW operation and the reflectivity characteristics of this surface-emitting laser have been investigated.