W. R. Wagner

Molecular beam epitaxial growth of uniform In0.53Ga0.47As on InP with a coaxial In‐Ga oven

Epitaxial layers of In0.53Ga0.47As lattice matched to InP substrates have been grown by molecular beam epitaxy. The (100) InP substrate surfaces were first oxide passivated and then thermally cleaned under 1.5×10−6 Torr of arsenic moleuclar beam exposure (i.e., 1.24×1014 As4/cm2 sec). When they were heated to 500 °C, damage‐free surfaces without oxygen and carbon contamination were obtained. The surface chemical composition as a function of the thermal cleaning temperature was studied with Auger electron spectroscopy. In0.53Ga0.47As epilayers of highly uniform composition were grown over a 7‐cm2 InP substrate using an In/Ga coaxial oven design. Reproducible In and Ga beam fluxes to obtain lattice‐match condition were achieved by adjusting the aperture ratio of the In and Ga reservoirs, and the oven temperature. Net electron concentration as low as 3×1015 cm−3 has been achieved for the In0.53Ga0.47As layers.

Photoluminescence study of acceptors in AlxGa1−xAs

A photoluminescence study of C, Si, Ge, Be, Mg, and Zn acceptors in AlxGa1−xAs is made. The binding energy of these acceptors is determined from the free‐to‐bound transitions at 75 K as a function of aluminum composition up to x∼0.4. It is observed that C, Be, and Mg behave like effective mass acceptors in AlxGa1−xAs while Si, Zn, and Ge show positive deviations from the effective mass theory with Ge exhibiting the maximum deviation. This difference in the behavior of the acceptors is suggested to be due to the difference in their central cell corrections in GaAs. The relative merits of these acceptors, in terms of their solubility, ionization energy, and diffusivity are considered. It is concluded that Mg is an attractive acceptor dopant in AlxGa1−xAs grown by liquid phase epitaxy.

Temperature dependence of photoluminescence of n‐InGaAsP

The temperature dependence (from 6 to 300 K) of the near band gap photoluminescence (PL) of n‐type InGaAsP is investigated. These layers, epitaxially grown on InP substrates, span the entire range of lattice matched compositions of the quaternary alloy. The spectral width of the PL emission and its temperature dependence are found not to vary with composition. However, compositional grading, especially evident at the center of the InGaAsP alloy range, often results in significant linewidth increase. These results are correlated with double crystal x‐ray diffraction measurements. The experimental results are compared with predictions of van Roosbroeck–Shockley formalism.

Effects of Ga(As,Sb) active layers and substrate dislocation density on the reliability of 0.87‐μm (Al,Ga)As lasers

Reliability data are presented for (Al,Ga)As double‐heterostructure lasers that emit light near 0.87 μm. Devices were grown with and without small additions of Sb to the active layer, with some devices grown on high dislocation density substrates. The reliability is more than an order of magnitude better for lasers with GaAs1−ySby active layers with y≊0.01 than for lasers with GaAs active layers. The rate of formation of dark line defects is reduced in the Ga(As,Sb) active layer lasers such that not all devices fail due to dark line defects. However, for Ga(As,Sb) active layer lasers grown on high dislocation density substrates, dark line defects formed very rapidly. An increase of roughly an order of magnitude in the substrate dislocation density resulted in a nearly three orders of magnitude decrease in the 70 °C lifetimes of Ga(As,Sb) active layer lasers.

Molecular‐beam epitaxial growth of uniform Ga0.47In0.53As with a rotating sample holder

Ga0.47In0.53As and Al0.48In0.52As were grown lattice matched to InP substrates with a rotating substrate holder. The Ga, In, and Al beams were supplied by separate effusion cells and the uniformity of the resulting layers was evaluated with x‐ray rocking curves for different rotation speeds. Lateral variation of the lattice constant as small as 10−5 per cm may be achieved with a rotation speed of 3 rpm. The full width at half‐maximum of the x‐ray spectrum from the epitaxial layer is comparable to that of the substrate indicating that there is practically no compositional grading.

Photoluminescence measurements in Ge‐doped p‐type Ga0.60Al0.40As

Results of photoluminescence and Hall effect measurements of p‐type Ge‐doped Ga0.60Al0.40As grown by liquid phase epitaxy are reported. The effective segregation coefficient for Ge for growth at 785 °C is estimated to be ∼2×10−3. The photoluminescence spectra at 5.5 K are characterized by two edge emission bands at ∼1.91 and ∼1.88 eV and a broadband at ∼1.55 eV. The edge emission bands are identified to be donor‐acceptor pair recombination bands involving the same donor but two different acceptors. The ionization energy of the donor is estimated to be 50–60 meV and the acceptor ionization energies are estimated to be ∼60 and ∼100 meV for the 1.91‐ and 1.88‐eV bands, respectively. The deep acceptor is believed to involve a background impurity, most likely C or Si. It is suggested that the 1.55‐eV band arises from a next‐nearest neighbor complex consisting of Ge on an arsenic site and an As vacancy. Post‐growth annealing treatment at 830 °C is found to decrease the photoluminescence intensity suggesting the...

Photoluminescence measurements in Ge-doped p-type Ga/sub 0. 60/Al/sub 0. 40/As

Results of photoluminescence and Hall effect measurements of p‐type Ge‐doped Ga0.60Al0.40As grown by liquid phase epitaxy are reported. The effective segregation coefficient for Ge for growth at 785 °C is estimated to be ∼2×10−3. The photoluminescence spectra at 5.5 K are characterized by two edge emission bands at ∼1.91 and ∼1.88 eV and a broadband at ∼1.55 eV. The edge emission bands are identified to be donor‐acceptor pair recombination bands involving the same donor but two different acceptors. The ionization energy of the donor is estimated to be 50–60 meV and the acceptor ionization energies are estimated to be ∼60 and ∼100 meV for the 1.91‐ and 1.88‐eV bands, respectively. The deep acceptor is believed to involve a background impurity, most likely C or Si. It is suggested that the 1.55‐eV band arises from a next‐nearest neighbor complex consisting of Ge on an arsenic site and an As vacancy. Post‐growth annealing treatment at 830 °C is found to decrease the photoluminescence intensity suggesting the...

Enhanced indium phosphide substrate protection for liquid phase epitaxy growth of indium‐gallium‐arsenide‐phosphide double heterostructure lasers

Thermal degradation of indium phosphide (InP) single crystal substrates prior to liquid phase epitaxy growth has been virtually eliminated by using an improved protection technique. The phosphorus partial pressure provided by a Sn‐In‐P solution localized inside an external chamber surrounding the InP substrate prior to growth prevents thermal damage to the surface. Nomarski contrast photomicrographs, as well as photoluminescence and x‐ray diffractometric measurements indicate that InP substrates protected by this method suffer a negligible deterioration, in contrast to the results of the more commonly used cover‐wafer method.

Stresses induced in GaAs by TiPt ohmic contacts

Measurements of the radius of curvature of GaAs substrates metallized with Ti–Pt bilayer thin films and annealed at 450 °C indicate that the state of stress of the substrate (tension versus compression) at the interface varies with the thickness ratio of the metals. Increasing thicknesses of Ti (Pt) result in increasing tensile (compressive) stresses in the substrate. An appropriate choice of the thickness ratio of Ti/Pt yields an unstressed substrate after annealing. It was found in most cases that extensive plastic deformation occurred in the film during annealing.

Anomalous polarization characteristics of 1.3‐μm InGaAsP buried heterostructure lasers

The stimulated emission from lasers with a linear light‐current characteristic is polarized in the TE mode. For some lasers with a kink in the L‐I curve, the kink represents the onset of a higher order TM polarized stimulated emission. Both TE and TM modes are present above the kink. These TE and TM emissions usually have separate groups of longitudinal modes. Under pulsed operation, the TE mode appears before the TM mode. X‐ray diffraction measurements suggest the presence of an internal stress in lasers exhibiting stimulated TM emission. A possible explanation for the observation is discussed. The mechanism is based on (i) higher optical gain of the TM mode than that of the TE mode in the presence of a compressive stress and (ii) larger reflectivity of the higher order TM modes. The power output at which a kink appears can be increased by decreasing the active layer width.