Hao-Hsiung Lin

Super-gain AlGaAs/GaAs heterojunction bipolar transistors using an emitter edge-thinning design

A novel emitter edge‐thinning structure was adopted for Npn Al0.5Ga0.5As/GaAs single heterojunction bipolar transistors grown by liquid phase epitaxy. In this structure, the emitter edge was etched down to approximately 0.1 μm thick such that the surface and emitter‐base junction depletion regions could touch each other. As a result, the current is blocked from the emitter periphery and the surface leakage current is reduced which improves the current gain especially at low operating current. The best device thus obtained shows a common emitter current gain of 12 500 at a collector current of 50 mA which is the highest gain reported to date for the heterojunction bipolar transistors. The current gain characteristics were indeed improved especially at a collector current below 10 μA.

Origin of high offset voltage in an AlGaAs/GaAs heterojunction bipolar transistor

The high offset voltage of an Npn AlGaAs/GaAs heterojunction bipolar transistor prepared by liquid phase epitaxy is proved to be equal to the turn‐on voltage difference between emitter‐base heterojunction and base‐collector homojunction. The potential spike at the emitter‐base heterointerface is experimentally confirmed by observing an activated transport process and a reachthrough effect under reverse operation. It is believed that the electron thermionic emission process plays an important role in determining the p‐n junction I‐V characteristics.

Nonlinear refractive‐index and two photon‐absorption near half the band gap in AlGaAs

The wavelength dependence of the nonlinear refractive index and two‐photon absorption coefficient near half the band gap was measured in an AlGaAs waveguide. The two photon figure of merit for efficient nonlinear optics in AlGaAs is shown to be quite favorable for photon energies less than one half the band gap.

Lumped-element compensated high/low-pass balun design for MMIC double-balanced mixer

We report a novel lumped element balun structure for both monolithic and hybrid circuit applications. The proposed structure utilizes two filters to compensate the amplitude and phase errors at the two balance outputs of a traditional out-of-phase power splitter. This circuit requires no multilayer or suspended substrates techniques; therefore, wide applications on many circuits operated especially, in the low microwave band, are expected. Two monolithic microwave integrated circuit (MMIC) mixers were built to demonstrate the electrical feasibility.

Transport theory of the double heterojunction bipolar transistor based on current balancing concept

The effect of the two‐interface conduction‐band spikes of a double heterojunction bipolar transistor on the current transport was theoretically studied. The model was based on the current‐balancing concept at both the emitter‐base and base‐collector heterojunctions. The analytical expressions for the current‐voltage characteristics and the offset voltage are derived and relate to material parameters. It is found that the back‐and‐forth bouncing of carriers between two potential spikes and the associated recombination loss represented by an important parameter ΔE0 play an important role in determining the transistor characteristics. The theory also reveals that in order to eliminate the offset voltage of a double heterojunction bipolar transistor, the emitter and the collector must have the same area, the electron injection efficiency at the base‐collector junction must be made close to unity, and the potential spike energy ΔE1 must be smaller than ΔE0.

Effect of InGaAs capping layer on the properties of InAs/InGaAs quantum dots and lasers

We report the effects of In0.33Ga0.67As capping layers on the structural and optical properties of InAs self-organized quantum dots grown by gas-source molecular-beam epitaxy. With different deposition methods for the InGaAs capping layer, the quantum-dot density can be adjusted from 2.3×1010 to 1.7×1011 cm−2. As-cleaved 3.98-mm-long diode laser using triple stacks of InAs quantum dots with the capping layer grown by GaAs/InAs sequential binary growth demonstrates an emission wavelength of 1305 nm and a threshold current density of 360 A/cm2. A ground-state saturation gain of 16.6 cm−1 is achieved due to the high dot density.

Highly strained 1.24-μm InGaAs/GaAs quantum-well lasers

Highly strained InGaAs/GaAs quantum wells grown at very low temperature (380 °C) have been studied. The critical thickness of the In0.38Ga0.62As quantum well is 8.8 nm and the photoluminescence peak is at 1.24 μm. An edge-emitting In0.388Ga0.612As/GaAs quantum-well laser demonstrates an emission wavelength of 1.244 μm at 18 °C. The threshold current density is 405 A/cm2 for an as-cleaved diode laser with 873-μm cavity length. The internal quantum efficiency and laser cavity loss are 93% and 6.4 cm−1, respectively.

Room-temperature 2.2-/spl mu/m InAs-InGaAs-InP highly strained multiquantum-well lasers grown by gas-source molecular beam epitaxy

We report the fabrication and performances of 2.2-/spl mu/m InAs-InGaAs-InP highly strained multiple-quantum-well (MQW) lasers grown by gas-source molecular beam epitaxy. The lasers operated at room temperature demonstrate a threshold current density of 900 A/cm/sup 2/ a maximum external quantum efficiency of 28%, and a maximum output power exceeding 60 mW per facet. To the best of our knowledge, this is the longest room-temperature emission wavelength reported for lasers grown on InP substrates to date. The effect of strain compensation on the quality of the InAs-In/sub x/Ga/sub 1-x/As MQWs was also studied using double crystal X-ray diffractometry and photoluminescence techniques. The experimental results reveal that there is no significant difference on the epilayer quality of the samples with strain compensation. However, the group V stable surface growth condition is indeed better than the group III stable surface growth condition on the epilayer quality.

Energy gap reduction in dilute nitride GaAsSbN

The energy gap of dilute nitride GaAsSbN has been studied. We found that the energy gap reduction induced by nitrogen incorporation is nearly independent of the Sb composition of the alloy, indicating that the conduction band and the valence band can be independently manipulated by incorporating N and Sb, respectively. A “double” band anticrossing (BAC) model, which is a combination of a BAC model for GaAsN and a valence BAC model for GaAsSb with the localized levels and hybridization parameters reported in literatures, has been proposed to fit the energy gap of annealed GaAsSbN samples. The as-grown samples, however, are with lower energy gaps, most likely resulting from the existence of substitutional N pairing and clustering in the alloys.

Growth of InAsN/InGaAs(P) quantum wells on InP by gas source molecular beam epitaxy

The growth of InAsN/InGaAs(P) quantum wells (QWs) on InP substrates by gas-source molecular-beam epitaxy and a rf plasma nitrogen source is reported for the first time. The double crystal x-ray diffraction satellite peaks of the InAsN/InGaAsP multiple quantum well (MQW) samples are sharper than those of the pure InAs/InGaAsP MQW samples, showing that a flatter heterointerface is achieved due to the smaller lattice mismatch. However, broadening of the satellite peaks and degradation of the photoluminescence (PL) intensity due to the increase of the nitrogen composition in these InAsN/InGaAsP MQWs suggest the existence of defects introduced by the small diameter nitrogen atoms located on arsenic sites. The PL result also shows that the peak energy decreases as the nitrogen composition increases. The estimated transition energy shrinkage coefficient is −31 meV/at. % nitrogen. The largest nitrogen composition obtained in this study is 5.9%, and its 10 K PL peak wavelength is ∼2.6 μm (480 meV). The effects of ...