Jen-Wei Pan

Theoretical study of the temperature dependence of 1.3-/spl mu/m AlGaInAs-InP multiple-quantum-well lasers

The temperature dependence of the differential gain, carrier density, and transparency current density for 1.3-pm Al- GaInAs-InP multiple-quantum-well lasers has been theoretically studied using the optical gain calculation from 250-380 K. The characteristic temperatures of the carrier density and differential gain at threshold are calculated to be 254 and 206 K, respectively. The Auger current density accounts for more than 50% of the total current density. The leakage current density exhibits the highest temperature sensitivity and becomes an essential part of the total current density at a high temperature. The calculated characteristic temperatures of the transparency and threshold current densities are 106 and 84 K, respectively, which agree well with the reported experimental results.

Formation of self-organized In0.5Ga0.5As quantum dots on GaAs by molecular beam epitaxy

Abstract Self-organized In 0.5 Ga 0.5 As quantum dots have been successfully grown on vicinal GaAs substrates by molecular beam epitaxy. The density of the quantum dots can be changed by nucleating the dots under different As overpressure. Substrate tilt angle of 15° results in much larger dot size and density than that of 4° due to the closely spaced step edges on the surface. Through investigations of the dots grown on In 0.1 Ga 0.9 As buffer, the strain energy of the buffer layer is also found to be an important factor that affects the size and density of the quantum dots.

Effect of column III vacancy on arsenic precipitation in low-temperature grown III–V arsenides

Separately grown p-type, intrinsic, and n-type GaAs at low temperatures as well as a combined p-i-n structure have been used to study the formation of As precipitates upon annealing at 800 °C. For the separate structures, least precipitates have been noticed in the n-type material. In contrast, the highest density of precipitates appears in the n region for the p-i-n structure. In addition, an obvious band depleted of precipitates, exists in the intrinsic region near the n-i interface. A general vacancy model, including Fermi level effect and crystal bonding strength (thermodynamic factor), has been developed to explain the current results as well as to predict As precipitation in various low temperature grown III–V heterostructures.

Suppression of electron and hole leakage in 1.3 μm AlGaInAs/InP quantum well lasers using multiquantum barrier

The slope efficiency and threshold current density of 1.3 μm AlGaInAs/InP lasers with AlInAs–AlGaInAs multiquantum barrier (MQB) are experimentally studied and compared with the conventional step-index separate confinement heterostructure (SCH) laser. With the MQBs at the guiding layers, the characteristic temperature can be improved as much as 10 K as compared with the conventional SCH laser. This is attributed to the suppression of electron and hole leakage currents.

Temperature-dependent characteristics of 1.3-μm AlGaInAs-InP lasers with multiquantum barriers at the guiding layers

Strain-compensated 1.3-/spl mu/m AlGaInAs-InP multiquantum-well (MQW) lasers with multiquantum barriers at both the n- and p-type guiding layers are comprehensively studied. The laser exhibits a characteristic temperature as high as 95 K and degradation in slope efficiency as low as -1.06 dB in the temperature range from 25/spl deg/C to 75/spl deg/C. The characteristic temperature of transparency current density is deduced to be 129 K. It is also found that the internal loss increases slowly with temperature, while the temperature dependence of the internal quantum efficiency dominates the degradation of the external quantum efficiency due to the degradation of the stimulated recombination, and significant increase of electron and hole leakage at high temperature.

Reduction of hole transit time in GaAs MSM photodetectors by p-type /spl delta/-doping

The temporal responses of the undoped, n-type, and p-type /spl delta/-doped GaAs metal-semiconductor-metal photodetectors were systematically studied. The full-width at half-maximum of the temporal response is significantly improved at low bias for the /spl delta/-doped detectors compared to the conventional undoped one. The p-type /spl delta/-doped detector exhibits the smallest fall-time, and hence the highest bandwidth, because the induced electric field in the absorption region facilitates the transport of the photo-generated holes. In addition, the p-type /spl delta/-doped detector also gives the highest peak amplitude of the temporal response. Two dimensional simulation on the internal electrical field distribution in the detectors is consistent with the experimental results.

Molecular‐beam epitaxial growth of InxAl1−xAs on GaAs

The surface reconstruction of InAlAs on GaAs between 490 and 700 °C has been investigated during molecular‐beam epitaxial growth. It is found that the surface reconstruction of InAlAs is similar to that of AlGaAs alloy. The (2×1) and (1×1) surfaces occur at a substrate temperature between 490 and 650 °C, while at a temperature above 650 °C, the ordered As‐stabilized (3×2 surface appeared during the steady‐state growth. InAlAs/GaAs heteroepitaxial layers have been analyzed and reveal that the residual strain in the epilayers is strongly dependent on the composition as well as the thickness of the epilayer. These characteristics are consistent with the InGaAs/GaAs system.

Characteristics of multistack multiquantum barrier and its application to graded-index separate confinement heterostructure lasers

The enhancement of electron barrier height by multistack multiquantum barrier structure is simulated using the transfer matrix method. The validity and feasibility of this concept is verified by the experimental results on GaAs-AlAs multistack multiquantum barriers. Based on the simulated results, both 0.78 and 1.3 /spl mu/m graded-index separate confinement heterostructure (GRIN-SCH) lasers with predicted enhanced carrier and optical confinements using graded multistack multiquantum barriers are designed. Lower threshold current, higher modulation bandwidth as well as higher characteristic temperature are expected for these lasers.

Characteristics of In0.3Ga0.7As/In0.29Al0.71As Heterostructures Grown on GaAs Using InAlAs Buffers

Device quality In0.29Al0.71As and In0.3Ga0.7As epilayers have been successfully grown on GaAs substrates using a carefully designed Inx Al1-x As multistage strain-relaxed buffer. Cross-sectional transmission electron microscopy has shown that the misfit dislocations are confined in the lower regions of the metamorphic buffer layer. The Hall electron mobility of the modulation doped structure grown on the InAlAs buffer was 6160 and 25379 cm2/V s with sheet carrier densities of 1.9×1012 and 1.8×1012 cm-2 at 300 and 77 K, respectively. The excellent characteristics of the field-effect transistors fabricated on this structure have indicated its potential for practical applications.

Strain-compensated 1.3-μm AlGaInAs quantum-well lasers with multiquantum barriers at the cladding layers

Strain-compensated 1.3-/spl mu/m AlGaInAs graded-index separate confinement heterostructure (GRINSCH) lasers with multiquantum barrier (MQB) at both the nand p-cladding layers are comprehensively studied and compared with the conventional GRINSCH lasers. It is found that the lasers with MQBs exhibit lower threshold current, higher maximum output power and better temperature characteristics because of the enhanced barrier height for carrier leakage. The characteristic temperature is improved as much as 10 K and the vertical far-field angle is also reduced from 38/spl deg/ to 32/spl deg/ as compared to the conventional counterpart.