S. W. Zehr

GaAs-AlGaAs tunnel junctions for multigap cascade solar cells

The growth and characterization of tunneling GaAs homojunctions and GaAs‐AlGaAs heterojunctions by molecular beam epitaxy for use as optically transparent interconnects in GaAs and AlGaAs solar cells is described. GaAs tunneling interconnects have been achieved with conductances of 300 A/cm2‐V at 0.050 V, and p‐AlxGa1−x As/n‐GaAs heterojunction structures with x up to 0.4 have been grown which have characteristics comparable to GaAs interconnects. Thin interconnects, 1000 A total thickness, have also been fabricated with conductances comparable to thicker junctions. The effect of dopant diffusion was found to be minimal at the 580 °C junction growth temperature, but annealing these tunnel junctions at 650 °C for several minutes caused diffusion of about 100 A distance.

Semi-insulating InP grown by low pressure MOCVD

Fe-doped semi-insulating InP layers have been successfully grown in a vertical flow, low pressure metalorganic chemical vapor deposition (LPMOCVD) system, and used as current blocking layers in buried crescent (BC) laser structures emitting at 1.51 µm. Triethylindium ((C2H2)3In), phosphine (PH3) and iron pentacarbonyl (Fe(CO)5) were used as the reactant gases. Process variables have been identified which produce high resistivity (107 to 108 Ω-cm) InP having featureless surface morphology, and layer thickness and doping uniformity. There is optical and x-ray diffraction evidence for the presence of an unidentified In-Fe-P second phase associated with markedly degraded surface morphology under nonoptimized growth conditions. Early BC lasers incorporating LPMOCVD grown, Fe-doped InP blocking layers have operated CW with threshold currents as low as 12 m A and optical output > 18 mW.

Selective growth of InP on patterned, nonplanar InP substrates by low-pressure organometallic vapor phase epitaxy

The effects of indium sources, mask materials and etched mesa profiles on growth mor-phology of Fe-doped semi-insulating InP on patterned, nonplanar InP substrates were studied for low-pressure organometallic vapor phase epitaxy (OMVPE). The presence or absence of polycrystalline InP layers deposited on the mask was found to depend on the indium source but not on the mask material. Trimethylindium was found to be the preferable indium source for prevention of polycrystalline InP deposits on the mask. The etched mesa shape was found to dominate the final geometry of the OMVPE re-grown InP layer. Inclusion of an interfacial layer of 1.16 µm bandgap wavelength InGaAsP between the dielectric mask and InP substrate produces a favorable mesa shape by con-trolling the level of undercut during mesa etching, so as to form a smooth mesa profile. After selective regrowth of InP over the resulting mesa, a planar surface is typically achieved for mesa stripes with a mask overhang length as long as 2.6 µm and a mesa height as high as 4 µm.

High‐speed and high‐power 1.3‐μm InGaAsP buried crescent injection lasers with semi‐insulating current blocking layers

The fabrication and performance of high‐speed and high‐power 1.3‐μm InGaAsP buried crescent lasers with semi‐insulating current blocking layers are reported. A modulation bandwidth of 11 GHz and acw output power of 42 mW/facet have been achieved. An approximate circuit model of the semi‐insulating buried crescent laser, which describes the effect of dc bias on parasitic capacitance at high‐speed operation, is also presented.

Growth and characterization of Fe‐doped semi‐insulating InP prepared by low‐pressure organometallic vapor phase epitaxy with tertiarybutylphosphine

Fe‐doped semi‐insulating InP epitaxial layers were grown by low‐pressure organometallic vapor phase epitaxy with tertiarybutylphosphine (TBP), triethylindium (TEI) and iron pentacarbonyl [Fe(CO)5] as the reactant gases. The growth was performed by varying the growth rate, growth pressure and V/III ratio. The epitaxial layers were characterized by optical microscopy, secondary ion mass spectrometry, double crystal x‐ray diffraction and current‐voltage measurements. Semi‐insulating InP epitaxial layers with specular surface morphology and low defect density were obtained at TBP partial pressure higher than 0.38 torr. A premature reaction between TEI and TBP was observed which presumably formed TEI:TBP adducts and/or polymers. As a result, the growth rate of Fe‐doped semi‐insulating InP layers grown at low pressure with TBP in our reactor decreased by 35% as the V/III ratio was increased from 15 to 46. Electrical measurements on these layers showed that the resistivity varied from 1.7×107 to 4×108 Ω cm as the V/III ratio was increased from 15 to 46. The resistivity of TBP‐grown materials is comparable to that of PH3‐grown materials over a measurement temperature range of 25–110 °C. Selective growth and surface planarization of Fe‐doped InP grown with TBP and trimethylindium on patterned etched mesas were achieved.Fe‐doped semi‐insulating InP epitaxial layers were grown by low‐pressure organometallic vapor phase epitaxy with tertiarybutylphosphine (TBP), triethylindium (TEI) and iron pentacarbonyl [Fe(CO)5] as the reactant gases. The growth was performed by varying the growth rate, growth pressure and V/III ratio. The epitaxial layers were characterized by optical microscopy, secondary ion mass spectrometry, double crystal x‐ray diffraction and current‐voltage measurements. Semi‐insulating InP epitaxial layers with specular surface morphology and low defect density were obtained at TBP partial pressure higher than 0.38 torr. A premature reaction between TEI and TBP was observed which presumably formed TEI:TBP adducts and/or polymers. As a result, the growth rate of Fe‐doped semi‐insulating InP layers grown at low pressure with TBP in our reactor decreased by 35% as the V/III ratio was increased from 15 to 46. Electrical measurements on these layers showed that the resistivity varied from 1.7×107 to 4×108 Ω cm as th...

Low threshold 1.51 μm InGaAsP buried crescent injection lasers with semi‐insulating current confinement layer

A hybrid growth technique has been used to fabricate low threshold 1.51 μm InGaAsP buried crescent injection lasers with a semi‐insulating current confinement layer. The technique involves a first stage of low pressure metalorganic chemical vapor deposition followed by a liquid phase epitaxy stage. The lasers exhibit cw threshold currents as low as 12 mA at 25 °C, high yield, differential quantum efficiency over 41%, and output power more than 18 mW. Small‐signal modulation response to 3.5 GHz has been obtained. The lasers show an initial small degradation rate of 1%/kh at 50 °C which gives an estimated operating lifetime of 47 years at 25 °C.

High quality Fe‐doped semi‐insulating InP epitaxial layers grown by low‐pressure organometallic vapor phase epitaxy using tertiarybutylphosphine

High quality Fe‐doped semi‐insulating InP epitaxial layers were grown by low‐pressure organometallic vapor phase epitaxy using tertiarybutylphosphine (TBP) and triethylindium (TEI) as the reactant sources. Semi‐insulating InP epitaxial layers with specular surface morphology and low defect density were obtained at TBP partial pressure higher than 0.38 Torr. Electrical measurements on these layers showed the resistivity of TBP‐grown materials to be comparable to that of PH3‐grown materials over a measurement temperature range of 25 to 110 °C. A premature reaction between TEI and TBP was observed upstream from the substrate in which things such as TEI:TBP adducts and/or polymers could have been formed. This reaction occurred under low pressure, high gas flow conditions which effectively suppressed analogous reactions for TEI:PH3. As a result, the growth rate of Fe‐doped semi‐insulating InP layers grown at low pressure with TBP in our reactor decreased by 35% as the V/III ratio was increased from 15 to 46.

Semi-insulating cobalt doped indium phosphide grown by MOCVD

A process is described for growing at least one layer doped with a transition element of cobalt on a substrate by introducing a source of indium, such as tri ethyl indium, (C2 H5)3 In or, a source of a group V element, a source of the transition element, such as cobalt nitrosyl tricarbonyl CO(NO)(CO)3, and a source of phosphorus, to the substrate heated in an inert or reducing atmosphere at a pressure substantially between 1/100 atmosphere and one atmosphere to grow at least one semi-insulating semiconductor layer on the substrate.

Low‐threshold and wide‐bandwidth 1.3 μm InGaAsP buried crescent injection lasers with semi‐insulating current confinement layers

A hybrid growth technique has been used to fabricate low‐threshold, high‐modulation bandwidth, and high‐power 1.3 μm InGaAsP buried crescent injection lasers. The technique involves a first growth of an Fe‐doped semi‐insulating current confinement layer by low‐pressure metalorganic chemical vapor deposition followed by a liquid phase epitaxy regrowth. The lasers have cw threshold currents as low as 10 mA at 25 °C, total differential quantum efficiency over 50%, high‐temperature operation up to 100 °C, and output power more than 33 mW/facet. A 3‐dB modulation bandwidth of 8.4 GHz has been achieved at 5 mW/facet.

Dynamic characteristics of semi‐insulating current blocking layers: Application to modulation performance of 1.3‐μm InGaAsP lasers

The dependence of current‐voltage (I‐V) characteristics on Fe‐doped semi‐insulating (SI) InP layer thickness has been investigated experimentally. The I‐V characteristics exhibit nonlinear behavior with ohmic, transition, and space‐charge‐limited regimes. An approximate circuit model of the buried crescent laser which describes the dynamic characteristics of the SI current blocking layers is presented. It is shown that for a 5‐μm‐thick SI layer, a very high resistivity of 4.9×108 Ω cm and a very low capacitance of 1 pF are obtained at the typical operating voltage for laser diodes of 1–2 V. Thus, semiconductor lasers with Fe‐doped SI InP current blocking layers offer great promise for achieving both wide modulation bandwidth and high‐power operation.