Jenn-Fang Chen

400-nm InGaN-GaN and InGaN-AlGaN multiquantum well light-emitting diodes

The 400-nm In/sub 0.05/Ga/sub 0.95/N-GaN MQW light-emitting diode (LED) structure and In/sub 0.05/Ga/sub 0.95/N-Al/sub 0.1/Ga/sub 0.9/N LED structure were both prepared by organometallic vapor phase epitaxy. It was found that the use of Al/sub 0.1/Ga/sub 0.9/N as the material for barrier layers would not degrade crystal quality of the epitaxial layers. It was also found that the 20-mA electroluminescence intensity of InGaN-AlGaN multiquantum well (MQW) LED was two times larger than that of the InGaN-GaN MQW LED. The larger maximum output intensity and the fact that maximum output intensity occurred at larger injection current suggest that AlGaN barrier layers can provide a better carrier confinement and effectively reduce leakage current.

High brightness green light emitting diodes with charge asymmetric resonance tunneling structure

In this work, we have applied the so called charge asymmetric resonance tunneling (CART) structure to nitride-based green light emitting diode (LED). From our CART LED, we observed an abrupt turn-on voltage near 2.2 V, and the forward voltage is around 3.2 V at 20 mA injection current. At 20 mA, the output power, and external quantum efficiency of the CART LED are about 4 mW, and 6.25%, respectively. The high brightness and efficiency green LED can be obtained by using the CART structure.

A Novel Dilute Antimony Channel

This letter reports, for the first time, a high-electron mobility transistor (HEMT) using a dilute antimony In0.2Ga0.8 AsSb channel, which is grown by a molecular-beam epitaxy system. The interfacial quality within the InGaAsSb/GaAs quantum well of the HEMT device was effectively improved by introducing the surfactantlike Sb atoms during the growth of the InGaAs layer. The improved heterostructural quality and electron transport properties have also been verified by various surface characterization techniques. In comparison, the proposed HEMT with (without) the incorporation of Sb atoms has demonstrated the maximum extrinsic transconductance gm,max of 227 (180) mS/mm, a drain saturation current density IDSS of 218 (170) mA/mm, a gate-voltage swing of 1.215 (1.15) V, a cutoff frequency fT of 25 (20.6) GHz, and the maximum oscillation frequency fmax of 28.3 (25.6) GHz at 300 K with gate dimensions of 1.2times200 mum2

\hbox{In}_{0.2}\hbox{Ga}_{0.8}\hbox{AsSb}/\hbox{GaAs}

Wavelength dependence of the reflectivity at an antireflection (AR) coated diode facet has been determined by comparing the spontaneous emission spectra obtained under the same bias condition before and after this facet is AR coated. Reliable measurements can be achieved by proper choice of the bias current.<<ETX>>

HEMT

An analytic expression for the tempoerature coefficient of the open‐circuit voltage has been derived in general, which may be applied to different kinds of p‐n junction solar cells. Based on the dominance of the saturation dark current density, the simplified expression have also been developed and justified by experimental measurements. It has been shown that the negative temperature coefficient of the open‐circuit voltage is decreased with the increasing light level and the interaction between minority carriers and the high‐low junction. Hence, the temperature coefficient of the open circuit voltage is good measure for providing a guide to test the effectivness of a high‐low junction in a back‐surface‐field (BSF) solar cell. Moreover, based on the measured temperature coefficient of the open‐circuit voltage from the BSF solar cells fabricated on thin epitaxial substrate, a new method for measuring the effective energy‐gap narrowing in the highly doped emitter has been proposed and studied. It has shown ...

Determination of wavelength dependence of the reflectivity at AR coated diode facets

The work reports a theoretical and experimental study on the device performance of near ultraviolet light-emitting diodes (LEDs) with specific design on the electron blocking layer (EBL) by employing the band-engineering. The simulation results show the polarization-induced downward band bending is mitigated in the specific EBL design and, hence, the capability of hole transportation increases and the behavior of electron overflow decreases. The experimental results show the LEDs with specific EBL design exhibited a reduction of forward voltage from 4.40 to 4.07 V and a much enhancement of light output power from 30.6 to 51.9 mW, compared with conventional LED.

Temperature coefficients of the open‐circuit voltage of p‐n junction solar cells

The conduction and interface states of laterally wet-oxidized GaAs-AlGaAs-GaAs structures after various oxidation times are investigated. Effective current blocking is achieved after 150min oxidation and the conduction of current through the oxidized AlGaAs layer is controlled by the Poole-Frenkel mechanism, from which a relative dielectric constant of 7.07 is obtained. At an oxidation time of 15min, capacitance-voltage spectra exhibit capacitance dispersion over frequency, implying the presence of an interface state. The intensity of the dispersion increases with increasing the oxidation time and admittance spectroscopy reveals a significant interface state at ∼0.28eV at 45min. Further increasing the oxidation time to 150min broadens the interface state to a set of continuous interface states from 0.19–0.31eV with decreasing densities from 3×1011to0.9×1011eV−1cm−2 and generates fixed charges of about 9.1×1011cm−2 in the oxidized layer. By comparison to a similar trap in a relaxed InGaAs∕GaAs, the interfa...

Hole Injection and Electron Overflow Improvement in 365 nm Light-Emitting Diodes by Band-Engineering Electron Blocking Layer

The growth by molecular-beam-epitaxy of high-quality 1.3 µm InGaAsN/GaAs quantum wells (QW) intra-cavity contacted vertical cavity surface emitting lasers (VCSELs) was demonstrated. Low-temperature growth, which suppresses the phase separation significantly improves material quality in the active region. Room-temperature continuous wave (RT-CW) single mode output power of 0.75 mW with an initial slope efficiency of 0.17 W/A and a side mode suppression ratio of 40 dB at a lasing wavelength of as long as 1304 nm were obtained.

Evolution of conduction and interface states of laterally wet-oxidized AlGaAs with oxidation time

Au, Cu, Ag, and Al are deposited on Te‐doped n‐GaSb layers directly grown on lattice mismatched GaAs semi‐insulating substrates. Sb4/Ga beam equivalent pressure ratios are found to profoundly influence the electrical properties of the Schottky diodes investigated here. The fact that both breakdown voltage and barrier height decrease with increasing Sb4/Ga ratios is attributed to the increase in surface state densities for samples grown at higher Sb4/Ga ratios. This suggestion is further confirmed by the model of surface state densities employing the relationship of barrier height to metal work function. The surface state densities are in the range of 2.3×1014 to 1.2×1015 states/cm2/eV corresponding to Sb4/Ga ratios of 2 to 9, respectively. X‐ray rocking peaks of samples grown at various Sb4/Ga ratios, and subsequently subjected to annealing, indicate different interactions at the interfaces which might support the observations.

Single Mode 1.3 µm InGaAsN/GaAs Quantum Well Vertical Cavity Surface Emitting Lasers Grown by Molecular Beam Epitaxy

According to the traveling wave rate equations, the carrier density inside a semiconductor laser is position dependent. This will introduce an additional wavelength shift for the radiation that experiences the largest gain. Analysis has led to the establishment of the relationship between the shift and the mean square deviation of the carrier density from its mean. Calculations show that under certain circumstances the shift may approach the order of 10/sup -1/ nm.<<ETX>>