Mao-Nan Chang

Line shape of electromodulation in uniform electric field of δ‐doped GaAs

The line shape of electromodulation in uniform electric field of δ‐doped GaAs has been calculated and compared with the experiments. The calculations show that the Franz–Keldysh oscillations (FKO) beats observed in experiments are contributed form the interference of heavy‐hole and light‐hole transitions. The calculations also show that the linear equation of extrema is a good approximation to analyze the electric field from the FKO line shape, although the equation only considers the heavy‐hole transition.

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.

High-reflectivity Pd∕Ni∕Al∕Ti∕Au ohmic contacts to p-type GaN for ultraviolet light-emitting diodes

Thermal stability, optical reflectivity, and contact resistivity of Pd∕Ni∕Al∕Ti∕Au ohmic contacts to p-type GaN were investigated. In contrast to its Pd∕Al∕Ti∕Au counterparts, Pd∕Ni∕Al∕Ti∕Au contacts retained their specific contact resistivity ( 76%) after long-term annealing at 150 °C in nitrogen ambient. According to the results of the secondary ion mass spectroscopy study, it is suggested that the Ni layer prevents the penetration of Ti into GaN during thermal treatment.

Low-resistance smooth-surface Ti/Al/Cr/Mo/Au n-type Ohmic contact to AlGaN/GaN heterostructures

A comparative study of the specific contact resistivity and surface morphology of Ti/Al/Ni/Au, Ti/Cr/Mo/Au, and Ti/Al/Cr/Mo/Au metal contact stacks on AlGaN/GaN heterostructures is reported. Compared to the conventional Ti/Al/Ni/Au contact, the Ti/Al/Cr/Mo/Au contact has much smoother surface and achieves minimum specific contact resistivity of 1.1×10−6 Ω cm2. This contact maintains its low contact resistivity after storage at 200 °C for 100 h in N2. The robustness of this contact is attributed to the Cr and Mo layers, which suppress the formation of Al–Au alloys in the contact stack.

Growth and characterization of crack-free semipolar {1-101}InGaN∕GaN multiple-quantum well on V-grooved (001)Si substrates

This work elucidates the two-stage growth of GaN on V-grooved (001)Si substrates using metal-organic chemical vapor deposition. The first growth stage proceeds on the {111}Si sidewalls until GaN fills the V grooves. Then the second stage continues and leads to a semipolar surface with the {1-101}GaN facets. GaN films with thickness of over 1μm can be obtained without cracks by this two stage-growth. Excitation-power-dependent and time-resolved photoluminescence measurements confirm that the internal electric field in the InGaN∕GaN multiple-quantum well (MQW) grown on this GaN template is indeed smaller than that of the MQW grown on (0001)GaN.

Crack-free GaN grown on AlGaN∕(111)Si micropillar array fabricated by polystyrene microsphere lithography

The authors report on the growth of GaN on AlGaN∕(111)Si micropillar array by metal-organic chemical vapor deposition. Using the substrates with micropillar array, 2-μm-thick GaN films without cracks can be achieved. Transmission electron microscopy, atomic force microscopy, and micro-Raman studies indicate that the dislocation density and residual stress of the GaN grown on micropillar array are also reduced. The results reveal the potential of this type of substrates for growing GaN-based devices as well as preparing GaN freestanding substrates.

A comprehensive study of Ge 1−x Si x on Ge for the Ge nMOSFETs with tensile stress, shallow junctions and reduced leakage

For the first time, growth of high-quality Ge-rich Ge<inf>1−x</inf>Si<inf>x</inf> (0≤x≤0.14) layers on Ge substrate was demonstrated. An effective suppression of the phosphorus diffusion in Ge<inf>1−x</inf>Si<inf>x</inf> and a better thermal stability of the nickel germanide on Ge<inf>1−x</inf>Si<inf>x</inf> were observed. A higher rectifying ratio with a reduced diode leakage current in n⁺-Ge<inf>1−x</inf>Si<inf>x</inf>/p-Ge<inf>1−x</inf>Si<inf>x</inf> is compared with n⁺-Ge/p-Ge. These results indicate that it is suitable for Ge<inf>1−x</inf>Si<inf>x</inf> to be used as source/drain (S/D) to fabricate the uniaxial tensile-strained channel Ge nMOSFETs.

POROUS SILICON LIGHT-EMITTING DIODE WITH TUNABLE COLOR

Abstract We successfully combined porous silicon and amorphous silicon together to fabricate a light-emitting diode, whose emitting color was tunable with different applied voltage. When the applied voltage increased from 30 to 90 V, the emitting color of the device could change from red to blue.

Effects of point defect distribution on arsenic precipitation in low-temperature grown III–V arsenides

The behavior of As precipitation in low-temperature grown III–V arsenides is investigated and correlated with the doping level, crystal bond strength, and dislocation density. Experimental results reveal that the doping level affects the concentration of charged defects, such as vacancy and antisite point defects, and hence leads to the selective precipitation of excess As in homojunctions. For heterostructures, As precipitates tend to condense in materials with a lower bond strength due to differences in point defect concentrations between the materials. In addition, dislocations are found to be a vacancy source that facilitates As precipitation around them. These results indicate that column III vacancies play an important role in As precipitation of low-temperature grown III–V arsenides.

Defects in metamorphic InxAl1−xAs (x<0.4) epilayers grown on GaAs substrates

Defects in Si-doped InxAl1−xAs (0<x<0.4) epilayers on GaAs substrates were systematically investigated by deep-level transient spectroscopy. Three electron traps, ranging from 0.22 to 0.89 eV, were observed in InxAl1−xAs grown by molecular beam epitaxy. Their energy levels can be extrapolated from those in the InxAl1−xAs/InP system. A low-temperature-grown buffer layer as well as thermal annealing were found to be capable of reducing the defects in the active layer effectively.