Jan J. Dubowski

Photoluminescence of gallium impurity in cadmium telluride

We have studied low‐temperature photoluminescence in CdTe containing Ga impurity in the 1.28–1.61 eV energy region. The impurity was introduced either by implantation of bulk CdTe wafers or by doping CdTe ingots during Bridgman growth. The presence of Ga was discovered and studied in epitaxial layers of CdTe grown on GaAs substrates by pulsed laser evaporation and epitaxy. Extra features caused by the Ga presence were observed in the edge emission and in the excitonic regions. Implantation results in extended mechanical damage, and only a small fraction of the implanted Ga is optically active. Samples doped during growth by the Bridgman technique exhibit changes in the excitonic region. The photoluminescence spectra of CdTe epitaxial films grown on GaAs exhibit features which are similar to those observed in bulk CdTe with Ga impurity.

X-ray photoelectron spectroscopy study of self-assembled monolayers of alkanethiols on (001) GaAs

Self-assembled monolayers of several alkanethiol molecules, with varying chain length and terminal groups, were investigated using x-ray photoelectron spectroscopy (XPS). The chain lengths varied from 10 to 15 methylene units, and the terminal group was either hydrophilic carboxylic acid and hydroxyl or hydrophobic methyl. The alkanethiol molecules were deposited on GaAs surfaces from liquid solutions. The impact of atmospheric exposure was examined by investigating one set of samples stored under atmospheric conditions and a second set that was stored in a nitrogen atmosphere prior to analysis. Carbon, oxygen, gallium, and arsenic core level XPS spectra were obtained on all surfaces. The intensity of the gallium and arsenic core levels indicates a considerable difference in the Ga∕As ratio dependent on the terminal group of the alkanethiol. Additionally, the carbon and oxygen spectra indicate varying chemical bonding on the surface with the alkanethiol’s having a carboxylic acid terminal group showing a ...

Monolithic multiple wavelength ridge waveguide laser array fabricated by Nd:YAG laser-induced quantum well intermixing

Maskless selective area cw Nd:YAG laser annealing of GaInAsP/InP quantum well (QW) structures has been investigated as a possible route towards the fabrication of monolithically integrated photonic circuits. Laser irradiation of a 5 QW laser structure, originally designed for lasers emitting at 1.52 μm, yielded material having a continuously changing band gap ranging from 1.52 to 1.4 μm over the distance of about 3 mm. Bars with arrays of ridge waveguide lasers, having cavity lengths from 300 to 600 μm, were fabricated from the processed material. An individual bar, 2–3 mm long, comprised lasers operating typically between 1.4 and 1.52 μm. The lasers showed stable threshold current density and high quantum efficiency at all operating wavelengths. The results indicate that the applied approach has the potential to realize the cost-effective fabrication of advanced photonic devices and photonic integrated circuits.

Laser-assisted dry etching ablation of InP

Abstract An XeCl excimer laser has been used to ablate InP in a Cl 2 /He environment. The chlorination of the surface of InP has been carried out at pressures of the reactive gas, p , between 15 and 40 mTorr. The saturation of the surface of the etched material with the product of reaction takes place at p > 18 mTorr, and for the laser pulse repetition rates ≤ 5 Hz the removal of material at rates from 0.02 to more than 0.4 nm/pulse has been achieved. Near atomically smooth surfaces have been observed if the thickness of the removed material did not exceed approximately 100 nm. The diffraction and interference effects, which depend on the state of the polarization of the laser beam and its coherence, have been observed to influence the surface morphology of material etched to depths greater than 100 nm. For linearly polarized light the formation of surface gratings with a period of Λ ≈ 0.25 μ m has been observed. Depth profiles of laser-etched craters indicated a strong dependence on the laser beam profile.

Optical properties of CdTe-Cd0.90Mn0.10Te multiple quantum well structures grown by pulsed laser evaporation and epitaxy

Abstract Low-temperature photoluminescence, photoluminescence excitation and Raman spectroscopy measurements of CdTeCd0.90Mn0.10Te multiple quantum well (MQW) structures grown by pulsed laser evaporation and epitaxy (PLEE) on (001) Cd1-xZnxTe substrates are carried out. The samples are grown from fluxes of Cd-Te and Cd-Mn-Te provided by ablation of solid CdTe and Cd0.93Mn0.07Te targets with Nd:YAG and excimer XeCl lasers, respectively. The excitonic lines corresponding to the quantum well E1-HH1 transition are investigated. Comparison between the observed PL excitonic emissions and calculated energy levels using a Kronig-Penney model with the well width as a fitting parameter allowed us to determine the “optical” well widths of the samples and to compare them with those determined from secondary ion mass spectroscopy in-depth profiles. Raman spectra for non-resonance excitation at 501.7 nm are dominated by the CdTe-like longitudinal optical (LO) modes at 166 cm-1 and MnTe-like LO modes at 194 cm-1 from the Cd0.90Mn0.10Te barriers. Under resonance conditions, with excitation at 476.5 nm the CdTe LO, 2LO and 3LO modes from the wells near 170,340 and 510 cm-1 dominate the spectra. The results clearly indicate that the PLEE-grown MQWs have the characteristics of the best currently available material.

XPS study of XeCl excimer-laser-etched InP

Abstract X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) have been applied to investigate the surface chemistry and morphology of InP wafers photochemically etched under 308 nm illumination from a XeCl excimer laser. The etching experiments were carried out at ambient temperature and in a low-pressure (1 μ bar) atmosphere of Cl 2 (10%) diluted in He. During the process, the samples were exposed to laser radiation with fluences of 73 mJ/cm 2 or 114 mJ/cm 2 . Both fluence values are below the ablation threshold of 140 mJ/cm 2 for InP. The mapping of the photoelectron spectral line intensities of In (3d 5/2 ), Cl (2p 3/2 ), and P (2p 3/2 ) displayed the distribution of In–Cl and In–P compounds on the surface of the wafer. The chemical composition and morphology of the etched surface were found to be dependent on laser fluence. Surfaces with a fine granular structure were observed at a lower fluence, while at higher fluences, surfaces with a linear grating-like structure were formed. More chlorine is bound to the surface prepared at a higher fluence.

Structure damage in reactive‐ion and laser etched InP/GalnAs microstructures

Etching of a chemical‐beam‐epitaxy‐grown InP/InGaAs multilayer structure with reactive ion etching (RIE) and laser‐assisted dry etching ablation (LADEA) is carried out in order to evaluate the extent of the damage induced by these two etching methods. Micro‐Raman spectroscopy indicates a systematic broadening of the phonon lines as a function of depth of a RIE fabricated crater. In contrast, LADEA which is based on the application of an excimer laser for the removal of the products of chemical reaction, shows no measurable changes in the phonon line widths when compared to as‐grown material. The results suggest that LADEA has potential for the photoresistless fabrication of damage free microstructures.

Raman scattering studies of Cd1−xMnxTe films grown on GaAs by pulsed laser evaporation and epitaxy

We have used Raman scattering to study a series of thin (111) Cd1−xMnxTe (CMT) films grown on (111) GaAs by pulsed laser evaporation and epitaxy. We show Raman spectra of CMT with 0.059≤x≤0.70, at 80 K. Samples with x≳0.4 exhibit up to 8th order combinations of CdTe‐like and MnTe‐like longitudinal optical phonons, which vary with excitation energy between 2.4 and 2.7 eV. We interpret these overtones as arising from outgoing resonance with the fundamental gap, and present an equation for the mth order phonon line intensity. We confirm the dependence of phonon frequency on x(Mn), and examine the variation of the phonon mode intensities with x(Mn). We also discuss the line widths of Raman and photoluminescence spectra versus x(Mn).

Epitaxial Growth Of Thin Semiconductor Films By Pulsed Laser Evaporation: Damage And Vaporization Of Cdte, Cd And Insb Targets Induced With Nd:Yag Laser.

The surface morphology of CdTe, Cd and InSb targets following vacuum pulsed laser evaporation has been examined. Vaporization of CdTe does not change the stoichiometric conditions of the surface, but precipitation of In is observed in the case of InSb. A stable vaporization rate can be obtained with a scanning laser beam after an initial layer of material is removed from the target and a characteristic surface structure is formed.

X-ray photoelectron spectroscopic study of KrF excimer laser nitrided InP surface

Nitridation of InP is performed by KrF excimer laser irradiation in an NH3 ambient. The N–In and N–P bonds are formed in the irradiated area in proportion to the number of laser pulses. The x-ray photoelectron spectroscopy spectra of the nitrided samples contain a small concentration of oxide components after aging in an air atmosphere than nonirradiated samples