W. G. Bi

Bowing parameter of the band-gap energy of GaNxAs1−x

We report a study of nitrogen incorporation in GaAs using a N rf plasma source. The N composition can be increased by lowering the growth temperature. X-ray diffraction shows no phase separation. Optical absorption measurements indicate that GaNxAs1−x is a direct band-gap material in the N composition range studied (x⩽14.8%), rather than a semimetal, contrary to theoretical predictions based on Van Vechten’s model. Analyzing the N composition dependence of the band-gap energy of the alloy indicates a composition-dependent bowing parameter, consistent with the first-principles supercell calculations [L. Bellaiche, S. H. Wei, and A. Zunger, Phys. Rev. B 54, 17 568 (1996)].

N incorporation in InP and band gap bowing of InNxP1−x

The N incorporation behavior in InP grown by gas‐source molecular beam epitaxy using a N radical beam source has been investigated. At a given growth temperature, the N composition in InNxP1−x is generally different from the N2 flow‐rate fraction in the vapor phase, and as the N2 flow‐rate fraction increases, it saturates after increasing to a certain point. This may be due to the small solubility of N in InP. Increasing the growth temperature will result in a loss of N incorporation into the InP as a result of the faster desorption of the N at high temperatures. Optical absorption measurements reveal that the band‐gap energy of InNxP1−x decreases drastically, resulting in band‐gap bowing.

Nanofabrication of 1-D photonic bandgap structures along a photonic wire

A strongly-guided one-dimensional (1-D) waveguide called a photonic wire has high spontaneous emission coupling efficiency, enabling one to realize low-threshold lasers. Combined with the use of 1-D photonic bandgap structures consisting of arrays of holes etched within the photonic wire, novel microcavity lasers can be realized. We report the nanofabrication of a photonic bandgap structure for 1.5 /spl mu/m wavelength along a InGaAsP photonic wire, and discuss numerical simulations for its electrodynamics.

Directional light output from photonic-wire microcavity semiconductor lasers

We have obtained directional light output from a recently realized InGaAsP photonic-wire microcavity ring lasers. The output was achieved by fabricating a 0.45-/spl mu/m-wide U-shape waveguide next to a 10-/spl mu/m diameter microcavity ring laser. The laser has a threshold pump power of around 124 /spl mu/W when optically pumped at 514 nm. It is comparable to the former structure without output coupling. The output coupling efficiency can be controlled carefully by choosing the spacing between the laser cavity and the waveguide.

Growth and characterization of InNxAsyP1−x−y/InP strained quantum well structures

In this work, we propose the material InNxAsyP1−x−y (InNAsP) on InP for long-wavelength laser applications, where the unique feature of the smaller lattice constant of nitrides together with the large electronegativity of nitrogen atoms has been utilized in reducing the system strain while increasing the conduction-band offset by putting N into a compressively strained material system. InNAsP/In(Ga)(As)P strained quantum well (QW) samples were grown by gas-source molecular beam epitaxy with a rf nitrogen plasma source. Very sharp and distinct satellite peaks as well as Pendellosung fringes are observed in high-resolution x-ray rocking curves for these QWs, indicating good crystalline quality, lateral uniformity, and vertical periodicity. Photoluminescence (PL) measurements on InNAsP/InP single QWs with different well widths as well as on InNAsP/InGaAsP multiple QWs reveal strong PL emissions in the range of from 1.1 to 1.5 μm, demonstrating their suitability for long-wavelength applications.

Improved high-temperature performance of 1.3-1.5-/spl mu/m InNAsP-InGaAsP quantum-well microdisk lasers

We report for the first time lasing action in the InNAsP-InGaAsP material system. Dramatic improvement in lasing action in a microdisk cavity was observed at elevated temperature up to 70/spl deg/C, which is about 120/spl deg/C higher than that of InGaAs-InGaAsP microdisk. This resulted in the first optically pumped InNAsP-InGaAsP microdisk lasers capable of above room-temperature lasing. The improvement of lasing temperature can be attributed to a large conduction band offset between the quantum well and barriers in the InNAsP-InGaAsP material system.

Observation of enhanced photoluminescence in erbium‐doped semiconductor microdisk resonator

We report experimental results from an erbium‐doped gallium phosphide microdisk resonator pumped by a Ti‐sapphire laser at 980 nm. Fabrication and characterization of the microdisk resonator are discussed. Enhanced Er+3 intra‐4f‐shell photoluminescence was observed in the microdisk resonator due to microcavity effect and compared to a thin film sample. At low pumping power intensity, the photoluminescence from erbium‐doped gallium phosphide microdisks is an order stronger than that from a thin film sample.

Growth studies of GaP on Si by gas-source molecular beam epitaxy

We report a growth study of GaP films grown by gas-source molecular beam epitaxy on Si substrates oriented 4° off (100) toward [110]. Reflection high-energy electron diffraction (RHEED), high-resolution X-ray diffraction rocking curve (XRC), and scanning electron microscopy (SEM) were used to characterize material quality. Growth studies were carried out in terms of the growth temperature, V/III ratio, and GaP film thickness. Two different growth methods were used : one-step direct growth and two-step growth, i.e. a thin GaP layer is grown first at a relatively low temperature as a buffer layer, followed by the main GaP layer grown at the normal growth temperature. The results show that with the two-step growth. the material quality of GaP can be greatly improved. Investigation of the effect of using different prelayers (As 2 , P 2 , Al, Ga, and Ga + Al) on the quality of GaP films reveals that the Ga prelayer gives the best result. By optimizing the growth conditions, GaP films with very smooth surfaces were obtained.

N incorporation in GaNxP1 − x and InNxP1 − x using a RF N plasma source

N incorporation in GaN x P 1-x and InN x P 1-x using a RF N plasma source We report a study of N incorporation behavior into GaP and InP as a function of growth conditions. With increasing N2 flow-rate fraction (N 2 flow rate over total group-V gas flow rate), the N composition increases up to a point but then saturates. This might be due to the small solubility of N in these materials or the leveling off of the active N species at higher N 2 flow rate. At a fixed N 2 flow-rate fraction, the higher the growth temperature T s is, the less N can be incorporated, which results from the lowering of the sticking coefficient of nitrogen at higher T s . Although the general trend of the growth condition dependence is the same for N incorporation in InP and GaP, the amount of N that can be incorporated is quite different. With GaP, N as high as 16% can be obtained, while with InP, only less than 1% can be incorporated. This is considered to be due to the very high equilibrium vapor pressure of N2 over InN compared to that over GaN.

In situ selective etching of GaAs for improving (Al)GaAs interfaces using tris-dimethylaminoarsenic

We have investigated the in situ chemical beam etching (CBET) process of (Al)GaAs using tris-dimethylaminoarsenic (TDMAAs) within a chemical beam epitaxy chamber. The optimal CBET condition of (Al)GaAs is established, according to the analysis of atomic force microscopy, capacitance–voltage carrier profiles, and current–voltage (I–V) measurements. This CBET process using TDMAAs is shown to provide a good etching selectivity (>20) of GaAs over AlxGa1−xAs (x⩾0.35) with a very smooth etched surface at the nanometer scale and a clean etched/regrown interface for regrowth applications. Improved I–V characteristics of etched/regrown p-n AlxGa1−xAs (x⩽0.35) junctions is also successfully demonstrated when the GaAs cap layer is preferentially etched first by TDMAAs before regrowth of AlxGa1−xAs.