Jung‐Kuei Hsu

AlGaAs/GaAs quantum wells with high carrier confinement and luminescence efficiencies by organometallic chemical vapor deposition

Single and multiple quantum wells with well widths ranging from 10 to 135 A were grown by atmospheric pressure organometallic chemical vapor deposition and characterized by photoluminescence (PL) and electrical measurements. Compared with single layers of high‐purity GaAs and AlGaAs which have high intensity near band‐edge excitonic transitions, the quantum well (QW) structures exhibit very strong luminescence of the discrete QW eigenstates. The intense QW signals indicate that the carrier confinement efficiency of the wells is very high, which is also supported by significant mobility enhancement in the samples. The sharp PL lines suggest high quality and smoothness of the well interfaces.

Pseudomorphic GaAs/InGaAs single quantum wells by atmospheric pressure organometallic chemical vapor deposition

High‐quality pseudomorphic GaAs/In0.12Ga0.88As single quantum wells (QW’s) were prepared by atmospheric‐pressure organometallic chemical vapor deposition. Photoluminesence spectra measured at 2.5 and 78 K exhibit intense, sharp peaks [full width at half‐maximum (FWHM)=2.6 meV for a 17‐A well at 78 K] from the quantized energy transitions of the QW’s. Peak positions agree well with a square well calculation that includes the strain‐induced band‐gap shift in the In0.12Ga0.88As. Quite unlike previous work with QW’s in which the FWHM was found to exponentially increase with decreasing well width, we observed a narrowing of the QW signals as the well width went below ∼30 A. In larger well samples (300 A), the onset of surface crosshatch patterns was observed, which is expected from critical thickness theory.

Exciton photoluminescence linewidths in very narrow AlGaAs/GaAs and GaAs/InGaAs quantum wells

A study of the low‐temperature photoluminescence characteristics of very narrow one‐dimensional quantum‐well structures, grown by atmospheric pressure organometallic chemical vapor deposition, is presented. Theoretically predicted narrowing of photoluminescence peaks as quantum‐well widths approach zero was experimentally observed in both AlGaAs/GaAs and strained GaAs/InGaAs samples. The role of such data in determining interface microstructure is discussed.

Reversal of light- and heavy-hole valence bands in strained GaAsP/AlGaAs quantum wells

Abstract We have experimentally determined the magnitude of the light-hole-heavy-hole exciton energy difference as a function of biaxial tensile strain in GaAsP/AlGaAs quantum wells using 5 K photoluminescence excitation spectroscopy. The strain is induced by the addition of phosphorus into the GaAs well layer which decreases its lattice constant so that it is less than that of the AlGaAs barrier material. Under certain conditions, the strain resulting from the lattice mismatch is large enough to reverse the order of the light- and heavy-hole valence bands. We found good overall agreement between the experimentally determined dependence of the light-hole-heavy-hole energy difference on the phosphorus concentration in the well layer and a simple calculation which included the effects of spatial confinement and biaxial tensile strain on quantum well exciton energies.

Tailoring of hole eigenenergies in strained GaAsP/AlGaAs single quantum wells grown by atmospheric pressure organometallic chemical vapor deposition

In this letter we present experimental results demonstrating the effects of tensile strain on the ground‐state hole eigenenergies of strained GaAsP/AlGaAs quantum wells (QWs) grown by organometallic chemical vapor deposition. Low‐temperature photoluminescence (PL) spectra exhibit sharp, intense peaks corresponding to the n=1 heavy and light hole related QW transitions. The relative positions of the peaks depend on both the strain and the width of the QWs. In wider wells (120 A), the lowest energy, and dominant PL peak was assigned to the light hole, and for a 80 A well, the heavy and light hole peaks merged.

Critical thickness of GaAs/InGaAs and AlGaAs/GaAsP strained quantum wells grown by organometallic chemical vapor deposition

In this paper we describe a study of strained quantum wells (QWs) as a means to experimentally observe the critical thickness (hc) for the formation of interfacial misfit dislocations. Two material systems were investigated: GaAs/In0.11Ga0.89As, in which the QW layers are under biaxialcompression, and Al0.35Ga0.65As/GaAs0.82P0.18, in which the QW layers are under biaxialtension. Samples were grown by atmospheric pressure organometallic chemical vapor deposition, and characterized by low-temperature photoluminescence (PL), x-ray diffraction, optical microscopy, and Hall measurements. For both material systems, the observed onset of dislocation formation agrees well with the force-balance model assuming a double-kink mechanism. However, overall results indicate that the relaxation is inhomogeneous. Annealing at 800–850° C had no significant effect on the PL spectra, signifying that even layers that have exceededhc and have undergone partial relaxation are thermodynamically stable against further dislocation propagation.

A new analytical technique of photoluminescence for optimization of organometallic chemical vapor deposition

An analytical method for quantitative interpretation of GaAs photoluminescence spectra was developed. Because of various transition mechanisms the photoluminescence spectrum of a sample may vary significantly under different measurement conditions. Based on a proposed scheme of transition priorities, spectra taken at various excitation powers were analyzed. Comparing results of undoped GaAs epitaxial layers grown by organometallic chemical vapor deposition under similar conditions but different V/III ratios, an optimum ratio corresponding to a minimum number of shallow impurities was clearly identified. Carbon and zinc were found to be the major shallow acceptors in most samples. At very low V/III ratios, carbon was the most dominant acceptor. The carbon concentration diminishes with an increasing ratio and the amount of zinc becomes more significant.

Effects of growth interruption on the optical properties of AlGaAs/GaAs and GaAs/InGaAs quantum wells grown by atmospheric pressure organometallic chemical vapor deposition

In this study, the effects of growth interruptions on Al0.17Ga0.83As/GaAs and GaAs/ InxGa1-xAs quantum wells (QWs) grown by organometallic chemical vapor deposition (OMCVD) were assessed using low-temperature photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. Growth interruption times were varied between 60, 10, and 0 sec. For both material systems, as the interruption time was reduced, the ground-state QW transition energies increased, while the linewidths of the peaks decreased. For the Al0.17Ga0.83As/GaAs structures, 5 K PL data suggests that the incorporation of impurities is enhanced by longer growth interruption times. In addition, as the interruption time was reduced, the energy separation between the 5 K PL and PLE peaks (Stokes shift) decreased, and was as low as 2.6 meV for no interruption. For GaAs/In0.11Ga0.89As samples, 2 K PL data indicated that the incorporation of donor species was not a function of the growth interruption time.

Effects of polyimide passivation on the photoluminescence of high‐purity epitaxial GaAs

Polyimide has been used as interlayer dielectric and passivation material. We studied the optical passivation property of polyimide by examining the spectral changes in the photoluminescence (PL) spectra of high‐purity epitaxial GaAs coated with polyimide. Before full cure, the polyimide is nearly transparent to visible and near‐infrared radiation. After full cure, the typical PL of GaAs was unobservable at liquid nitrogen or higher temperatures, but clear and distinct at liquid‐helium temperature. The resolution of the GaAs exciton spectrum was improved in the coated sample. The polyimide‐GaAs system also resulted in very weak luminescence extending over a wide spectral range from the red to near infrared.

Critical Thickness of GaAs/InGaAs and AlGaAs/GaAsP Quantum Wells Grown by Atmospheric Pressure OMCVD

A critical layer thickness study of strained GaAs/InGaAs and AlGaAs/GaAsP quantum wells (QWs) grown by atmospheric pressure organometallic chemical vapor deposition (OMCVD) is reported. Characterization by conventional photoluminescence (PL), photoluminescence excitation (PLE) spectroscopy, optical microscopy, and x-ray diffraction suggests that partial or regional relaxation begins to occur at critical thicknesses predicted by the force-balance model. To test the stability of strained quantum wells with well width near or exceeding the predicted critical thickness, annealing up to 850°C for ten minutes was carried out. No sign of degradation or complete relaxation of the QW layers was observed.