Daivasigamani Krishnamurthy

Growth and photoluminescence properties of TlInGaAsN/TlGaAsN triple quantum wells

TlInGaAsN/TlGaAsN system was proposed to fabricate the temperature-insensitive both lasing wavelength and threshold current density laser diodes, which are important in the wavelength division multiplexing optical fiber communication system. The effects of indium and nitrogen concentrations in the quantum wells (QWs) and barriers on the properties of molecular-beam epitaxy grown TlInGaAsN/TlGaAsN triple QWs (TQWs) were investigated. The TQW samples having higher N concentration in the QWs have the highest Tl incorporation without deterioration of the crystalline quality. The temperature dependence of the photoluminescence (PL) peak energy was found to be the least for the highest Tl containing TQW sample. The incorporation of Tl causes the reduction in the coupling constant of the electron–phonon interaction, leading to the reduced temperature dependence of the PL peak shift. Thermal activation energies, which are deduced from the Arrhenius plot of PL intensity, are attributed to the delocalization of the...

X-ray photoelectron spectroscopy analysis of TlInGaAsN semiconductor system and their annealing-induced structural changes

TlInGaAsN thin films grown by gas-source molecular-beam epitaxy were investigated by x-ray photoelectron spectroscopy (XPS) to analyze the Tl incorporation and to study the annealing-induced transformation of the atomic configurations. XPS analysis revealed that the Tl composition in the grown TlInGaAsN is around 1.5% and that the dominant atomic configuration of the TlInGaAsN changes from the In–As and Ga–N bonds to the In–N and Ga–As bonds by 700 °C rapid thermal annealing. High-resolution x-ray diffraction and reciprocal space mapping measurements showed that no significant out-diffusion of the elements occurs in the TlInGaAsN/TlGaAsN quantum wells (QWs) even after the same annealing. It is concluded that the blueshift in the photoluminescence peak for the TlInGaAsN/TlGaAsN QWs after annealing is attributed to the transformation of the atomic configuration in TlInGaAsN.

Optical properties of InGaPN epilayer with low nitrogen content grown by molecular beam epitaxy

The effect of nitrogen concentration on the optical properties of InGaP(N) epilayer was investigated. The temperature dependence of the photoluminescence (PL) peak energy of InGaPN (N = 1%) epilayer around room temperature was found to be almost one-half of that of InGaP epilayer. The incorporation of N causes the reduction of the coupling constant for the electron–phonon interaction, leading to the reduced temperature dependence of the PL peak shift. Thermal activation energy, which is deduced from the Arrhenius plot of PL intensity, was decreased by N incorporation. The reduced PL quenching is discussed in terms of the changes in the band alignment at the InGaPN/GaAs heterointerface by the increase in the N concentration.

Growth and characterization of TlInGaAsN/TlGaAsN triple quantum wells on GaAs substrates

TlInGaAsN/TlGaAsN triple quantum wells (TQWs) with different In and N concentration in the quantum wells (QWs) and barriers were grown by gas-source molecular beam epitaxy. The higher Tl incorporation was obtained for the TlInGaAsN/TlGaAsN TQWs having higher N concentration in the QWs region. Temperature dependencies of the photoluminescence (PL) spectra for the TlInGaAsN /TlGaAsN TQWs with different Tl incorporation in active region were compared and studied. Reduction in the temperature dependence of the PL peak energy was observed by increased Tl incorporation in the active region.

Synthesis and characterization of Gd-doped InGaN thin films and superlattice structure

Rare-earth (Gd) doped InGaN films and superlattices (SLs) were synthesized by electron cyclotron resonance (ECR) plasma-assisted molecular beam epitaxy (MBE) in the pursuit of new functional diluted magnetic semiconductors (DMSs). X-ray diffraction profiles of InGa(Gd)N epilayers indicated no phase separation with the avoidance of InN and GdN formation. Gd incorporation into the epilayers was confirmed by electron probe microscope analyzer. Local structure around the Gd atom was investigated by XAFS measurement using Gd LIII edge. It was shown that Gd atoms were mainly incorporated into the Ga sites in the InGaGdN epilayers.

Studies on TlInGaAsN double quantum well structures

In the pursuit of devices with reduced temperature-dependent emission wavelengths, TlInGaAsN double quantum well (DQW) structures with different barriers were grown on GaAs substrates by MBE and investigated. Although TlGaAsN barriers gave rise to higher Tl incorporation, as compared to TlGaAs barriers, the presence of lot of dislocations and very rough interfaces reduced the PL characteristics. The TlGaAsN barrier layer was modified with different combinations and the resultant samples are analyzed by SIMS, HRXRD, X-TEM and PL measurements. DQW Structures with combined barriers of TlGaAsN+TlGaAs+TlGaAsN and that with reduced N%-TlGaAsN barrier samples showed improved crystalline characteristics.

Quinary TlGaInNAs DQW Structures: Effect of Growth Temperature and Growth Rate on Tl Incorporation

TIGalnNAs-based DQW structures grown at various growth parameters were studied by secondary ion mass spectroscopy (SIMS). Enhanced Tl incorporation could be obtained using TlGaNAs barriers. A direct relationship between the Tl incorporation and N composition is clearly established by the analysis of the effect of growth temperature, growth rate, ECR power and nitrogen flow rate. The Tl incorporation increased with the increase of Tl flux in the case of DQW structures with TlGaAs barriers. In the case of DQW structures with TIGaNAs barriers, the Tl incorporation reached saturation at some Tl flux, indicating the N enhanced higher Tl incorporation.

MBE Growth of TlInGaAs/TlInP/InP SCH LDs and Their Laser Operation

TlInGaAs/TllnP/InP separate confinement heterostructures (SCHs) were grown by gas-source molecular-beam epitaxy and metal stripe laser diodes (LDs) were fabricated. Temperature variation of electroluminescence peak wavelength was as small as 0.06 nm/K due to the reduced temperature variation of band gap energy of TlInGaAs. Pulsed laser operation was achieved at 77 K - 297 K. Threshold current density for the TlInGaAs/TlInP/InP SCH LD (0.6 kA/cm2 at 77 K) was smaller than that for the TlInGaAs/InP double heterostructure LD (0.8 kA/cm2 at 77 K), which is due to the increased refractive index for TlInP and the improved optical confinement. Temperature variation of main peak wavelength in the lasing spectra was as small as 0.07 nm/K, which is much smaller than those for the InGaAsP/InP Fabry-Perot LDs (0.4 nm/K) and distributed feed-back LDs (0.1 nm/K)