Galvanic corrosion effects in InP-based laser ridge structures

Galvanic corrosion effects in metallized III-V laser structures have been studied. Small gaps present in the metallization can leave exposed semiconductor regions, which are susceptible to localized corrosion in the presence of an electrolyte. Electochemical measurements in two different electrolytes, i.e., 1% HF and concentrated H₃PO₄, were made of test structures comprised of n-type InP, p-type InP, and p-type InGaAs, as well as Au. Polarization measurements were made in all cases relative to a Ag/AgCl reference electrode. Corrosion potentials, measured relative to Au, of 540, 180, and 330 mV were obtained for n-type InP, p-type InP, and p-type InGaAs, respectively, in 1% HF. Values of 415, 47, and 138 mV were obtained for n-type InP, p-type InP, and p-type InGaAs, respectively, in concentrated H₃PO₄. Galvanic current densities of 2.0 × 10⁻⁶A/cm², 1.0 × 10⁻⁷ A/cm², and 4.0 × 10⁻⁶ A/cm² were obtained for galvanic couples of n-type InP/Au, p-type InP/Au, and p-type InGaAs/Au, respectively, in 1%HF. Values of 1.2 × 10⁻⁶ A/cm², 1.2 × 10⁻⁷ A/cm², and 1.0 × 10⁻⁶ A/cm² were obtained for galvanic couples of n-type InP/Au, p-type InP/Au, and p-type InGaAs/Au, respectively, in concentrated H₃PO₄. Complementary microstructural studies, using scanning electron microscopy, were done on actual metallized ridge laser structures, consisting of a p-type InP ridge with a p-type InGaAs capping layer and a Ti/Pt/Au metallization. Localized pitting of the InGaAs layer was observed for samples with gaps in the metallization.     

Studies of liquid-phase deposition-oxide/InP structure by liquid-phase deposition

Silicon-dioxide (SiO₂) growth on an indium-phosphide (InP) substrate by use of room-temperature (∼30°C) liquid-phase deposition (LPD) is demonstrated. The produced LPD-SiO₂ is of good quality and reliability because of the suppression of interdiffusion by use of relatively low temperatures. Because LPD is difficult without residual OH on the substrate, an InP surface rich in hydroxyls (In-OH) is created by pretreating the wafer substrate in a (29% NH₄OH:H₂O₂=1:1) solution. The LPD-SiO₂/InP is used to fabricate a metal-oxide semiconductor (MOS) capacitor with a device area of 1.12×10⁻⁴ cm², yielding a leakage-current density of 8.1×10⁻⁹ A/cm² at 3 MV/cm. A mechanism for the LPD deposition of SiO₂ on InP is also presented.     

InP growth and properties

Bulk polycrystalline InP is synthesized from the elements via a gradient freeze process. Hall data for a typical boule are N_d-N_a= 4.7 × 10¹⁵/cm³ and Μ77 = 28,000 cm²/V-sec. Photoluminescence data indicate that zinc is present as an acceptor impurity in the polycrystalline InP and in nominally undoped LEC single crystals grown using the synthesized InP as charge material. A series of doping experiments have determined the effective segregation coefficient to be 1.6 × 10⁻³ for Fe in InP. Semi-insulating InP crystals with resistivity > 10⁷ ohm—cm have been grown consistently from melts doped with 150 ppm Fe.     

Liquid encapsulated czochralski pulling of InP crystals

The growth of bulk indium phosphide crystals via liquid encapsulated Czochralski pulling from both stoichiometric and nonstoichiometric melts is described. Nominally un-doped crystals with carrier concentration N_D-N_A = 6 × 10¹⁵ cm⁻³ and Hall mobilities of 4510 cm²/Vsec at room temperature were grown. Also, we prepared Zn-or Cd-doped p-type crystals in the range 10¹⁶ ≤ N_A-N_D ≤ 10¹⁸ cm⁻³ with Hall mobilities ≤ 130 cm²/Vsec and Sn-doped n-type crystals in the range 4 × 10¹⁷ ≤ N_A-N_D ≤ 10¹⁸ cm^-3 with Hall mobilities ≤ 2400 cm²/Vsec. The dislocation density of LEC pulled InP crystals is typically ~ 10⁴ cm⁻².     

InP-on-CdS thin film heterostructures

Thin films of InP were deposited on single crystals and thin films of CdS by the planar reactive deposition technique. Good local epitaxy was observed on single crystals of CdS as well as InP and GaAs. The electrical evaluation of unintentionally doped films on semi-insulating InP substrates show them to be n-type with room temperature electron concentrations ranging from 5 × 1016 cm⁻³ to 5 × 10¹⁷ cm⁻³ and mobilities up to 1350 cm²/Vsec. For films intentionally doped with Mn and Be, p-type films were obtained. For Mn doping (deep acceptor level), room temperature mobilities as high as 140 cm²/Vsec and free carrier concentrations as low as 5 × 10¹⁶ cm⁻³ (with dopant level of 3 × 10¹⁸ cm⁻³) were obtained. For Bedoped films, free carrier concentrations of about 5 × 10¹⁸ cm⁻³ and mobilities of 20 cm²/Vsec were found. Scanning electron microscope and microprobe pictures show appreciable interdiffusion between the InP/CdS thin-film pair for InP deposited at 450°C. The loss of Cd from the CdS and the presence of an indium-cadmium-sulfur phase at the InP/CdS interface were observed. Interdiffusion is alleviated for InP deposition at lower temperatures. Supported in part by ERDA and AFOSR.     

The growth of low dislocation densityp-lnP single crystals

High qualityp-type InP is critical for devices ranging from high power injection lasers to space-based solar cells. The growth of 50 mm diameter, low defect density,p-type, Zn:InP substrates has been achieved for the first time at doping levels below 10¹⁸ cm⁻³. The 600 gram 〈111〉 B-seeded crystals were grown by the vertical dynamic gradient freeze technique. Dislocation densities are more than an order of magnitude below those achieved in comparable LEC-growth material. These range from 300 cm⁻² at the seed end to 1200 cm⁻² in the 50 mm diameter portion of the crystal. Single crystals were grown with carrier concentrations ranging from 1–5 × 10¹⁷ cm⁻³ as determined by Hall measurements. Hole mobilities as high as 100 cm² volt⁻¹ sec⁻¹ were achieved. The in-corporation of the zinc dopant follows normal freezing and a distribution coefficient of 0.67 ± .09 was determined. Infrared transmission imaging shows a lower level of stria-tion contrast relative to that observed for sulfur doped InP.     

Advances in LEC growth of InP crystals

By reducing the temperature gradients in the vicinity of the crystal-melt interface, 35-mm-diameter InP boules with much reduced dislocation densities have been grown by the liquid-encapsulated Czochralski technique. A reduction in the residual donor concentration of InP grown by this technique has been achieved by using In-rich charges prepared by adding elemental In to polycrystalline InP ingot material. Nominally undoped crystals with carrier concentrations as low as 1–2 x₄ 10¹⁵ Cm − 1 and 77 K mobilities as high as 7.0 × 10 cm² V⁻¹ s⁻¹ have been obtained. By growing doped crystals at increased seed or crucible rotation rates, short-range longitudinal variations in dopant concentration have been reduced to a few per cent, as determined by optical absorption measurements with a scanning CO₂ laser.     

Zn-doping in OMVPE Grown lnP:Zn/lnGaAs/lnPp-i-n double heterojunctlons with lnGaAs:Zn contacting layers

We report on the control of zinc in organometallic vapor phase epitaxial (OMVPE) grown InP:Zn/InGaAs/InPp- i- n double heterojunctions with InGaAs:Zn contacting layers. As a function of diethylzinc (DEZn) flow, we measure net acceptor concentrations for the InP:Zn p-layer in the range 2 × 10¹⁷≤N _a−N _d≤ 9 × 10¹⁷ cm⁻³. A 435°C post-growth anneal for 300 sec increases the net acceptor concentrations by a factor of 3.6 − to 6 × 10¹⁷≤N _a−N _d≤ 3 × 10¹⁸ cm⁻³. When the annealed value ofN _a − N_din the InP:Zn layer is 6 × 10¹⁷ cm⁻³ , secondary ion mass spectrometry (SIMS) measurements show abrupt Zn-doping transitions at the heterojunction interfaces. In contrast, when the annealed value ofN _a − N_din the InP:Zn layer is near the saturation value of 3 × 10¹⁸ cm⁻³, SIMS measurements show significant movement of Zn into the nominally undoped InGaAs instrinsic layer. Increasedp-i-n diode capacitance is associated with the Zn movement.     

High-speed InP/lnGaAs heterojunction bipolar transistor utilizing nonalloyed contacts on n+-InP contacting layers

We have demonstrated a high-speed InP/lnGaAs heterojunction bipolar transistor with nonalloyed TiPtAu contacts on n⁺-InP emitter and collector contacting layers. The use of SiBr₄ as a silicon doping source enabled the formation of low resistance (p_c <2 × 10⁻⁶Ω. cm²), nonalloyed TiPtAu contacts to the heavily doped (n = 2 × 10¹⁹ cm⁻³) InP contacting layers. A device with a 3 × 10 Μm² emitter contact exhibited excellent dc characteristics and had ƒ_T = ƒ_max = 107 GHz. Emitter and collector resistances are compared to a device with InGaAs contacting layers.     

The effect of a continuous etch on the growth rate and morphology of InP prepared by the vapor phase epitaxial-hydride method

A study of the effect of a continuousin situ etch of HC1 on growth rate and the properties of epitaxial InP layers prepared by the vapor phase epitaxial-hydride technique is reported. Growth rates were determined as a function of the following variables: HC1 flow rates in the mixing and source zones, PH₃ flow rates, and mixing zone temperatures. Epitaxial InP structures with good morphology were obtained when the continuous HC1 etch was varied between 0.8 and 1.5 cc/min. The average values (77K) of the carrier concentrations and mobilities were 1.3 × 10¹⁵ cm^s−3 and 23,000 cm²V^−l Sec⁻¹, respectively. The study indicates that the continuousin situ HCl etch improves the quality of epitaxial InP layers.     

Capacitance-Voltage characteristics of metal-insulator-semiconductor diodes with S passivation and Si interface control layers on GaAs and InP

GaAs and InP surfaces have been prepared by gas-phase and liquid-phase polysulfide passivation techniques followed by the deposition of Si interface control layers (ICLs) by e-beam evaporation. For GaAs surfaces, the performance of an ICL consisting of 1.5 nm Si on top of 0.5 nm of Ge has also been evaluated. Metal-insulator-semiconductor diodes with aluminum top electrodes were fabricated on these surfaces using silicon nitride deposited by a remote plasma-enhanced chemical vapor technique or silicon dioxide deposited by a conventional direct plasma-enhanced chemical vapor deposition technique. The quality of the interfaces was analyzed by capacitance-voltage (C-V) measurements and the interface state densities D_it were deduced from the C-V data using the high-low method. Values as low as 1.5 × 10¹² eV⁻¹cm⁻² were obtained for polysulfide-passivated GaAs surfaces with a Ge-Si or Si ICL, the lowest ever demonstrated using the high-low method for an ex-situ technique not involving GaAs epitaxy. For InP, the Si ICL does not reduce D_it below that of 2 × 10¹² eV⁻¹ cm ⁻² that was obtained for the polysulfide passivated surface. The Si ICL produces an interface that degrades more slowly on exposure to air for both GaAs and InP.     

Liquid phase epitaxial growth of ZnxCd1−xSnP2 on InP

The chalcopyrite alloy Zn_xCd_1−xSnP₂ is a potentially use-ful electronic material. In addition to having effective masses lower than and energy gaps similar to its III-V compound analogs, this alloy can also be lattice matched to InP. We have used an open-tube, sliding-boat, liquid-phase system to grow Zn_xCd_1−xSnP₂ epitaxially on InP sub-strates. Unintentionally-doped layers have electron con-centrations as high as 3 × 10¹⁹cm⁻³ with mobility values of about 2,000 cm²/V-sec. These mobility values are sub-stantially larger than have been obtained in the equivalent III-V materials at similar concentrations.     

Pd/Sb(Zn) and Pd/Ge(Zn) ohmic contacts on p-type indium gallium arsenide: The employment of the solid phase regrowth principle to achieve optimum electrical and metallurgical properties

The development of two metallizations based on the solid-phase regrowth principle is presented, namely Pd/Sb(Zn) and Pd/Ge(Zn) on moderately doped In_0.53Ga_0.47As (p=4×10¹⁸ cm⁻³). Contact resistivities of 2–3×10⁻⁷ and 6–7×10⁻⁷ Ωcm², respectively, have been achieved, where both systems exhibit an effective contact reaction depth of zero and a Zn diffusion depth below 50 nm. Exhibiting resistivities equivalent to the lowest values of Au-based systems in this doping range, especially Pd/Sb(Zn) contacts are superior to them concerning metallurgical stability and contact penetration. Both metallizations have been successfully applied for contacting the base layer of InP/In_0.53Ga_0.47As heterojunction bipolar transistors.     

Plasma anodization of evaporated Al-InP systems

Aluminium oxide-InP structures were fabricated by plasma anodization of evaporated Al-InP systems with intention of fabricating InP MISFETS. It was found that the resistivity and break-down strength of the A1₂O₃ film were influenced by the selection of the end point of the anodization. At appropriate conditions the resistivity of 5 × 10¹⁰ − 10¹²Ω cm for the anodic Al₂O₃ and the minimum density of the interface trap states of 4 × 10¹¹ cm⁻² ev⁻¹ for Al₂ O₃ -InP systems were obtained.     

Low pressure metalorganic chemical vapor deposition of InP and related compounds

The low pressure metalorganic chemical vapor deposition epitaxial growth and characterization of InP, Ga_0.47In_0.53 As and Ga_xIn_1-xAs_yP_1-y, lattice-matched to InP substrate are described. The layers were found to have the same etch pit density (EPD) as the substrate. The best mobility obtained for InP was 5300 cm² V⁻¹S⁻¹ at 300 K and 58 900 cm² V⁻¹ S⁻¹ at 77₂K, and for GaInAs was 11900 cm² V⁻¹ S⁻¹ at 300 K, 54 600 cm² V⁻¹ S⁻¹ at 77 K and 90 000 cm V⁻¹S⁻¹ at 2°K. We report the first successful growth of a GaInAs-InP superlattice and the enhanced mobility of a two dimensional electron gas at a GaInAs -InP heterojunction grown by LP-MO CVD. LP MO CVD material has been used for GaInAsPInP, DH lasers emitting at 1.3 um and 1.5 um. These devices exhibit a low threshold current, a slightly higher than liquid phase epitaxy devices and a high differential quantum efficiency of 60%. Fundamental transverse mode oscillation has been achieved up to a power outpout of 10 mW. Threshold currents as low as 200 mA dc have been measured for devices with a stripe width of 9 um and a cavity length of 300 um for emission at 1.5 um. Values of T in the range 64–80 C have been obtained. Preliminary life testing has been carried out at room temperature on a few laser diodes (λ = 1.5μm). Operation at constant current for severalthousand hours has been achieved with no change in the threshold current.     

Improved electrical properties on the anodic oxide/InP interface for MOS structures

The interface properties of the anodic oxide/n-type (111) InP metal oxide semiconductor (MOS) structures significantly improved while using the polishing agent HBr:K₂Cr₂O₇:H₂O (BCA). Annealing at 250°C dehydrates the grown oxides and has a strong effect on the surface potential. Composition of the oxides analyzed using x-ray photoelectron spectroscopy showed that the oxides are composed of In₂O₃, InPO₃, and InPO₄. MOS structures fabricated on BCA polished substrates show a lower surface state density of 6 × 10¹⁰ cm⁻² eV⁻¹ when compared to the substrates polished with bromine-methanol (8 × 10¹⁰ cm⁻² eV⁻¹).     

MeV energy sulfur implantation in GaAs and InP

Room temperature and elevated temperature sulfur implants were performed into semi-insulating GaAs and InP at variable energies and fluences. The implantations were performed in the energy range 1–16 MeV. Range statistics of sulfur in InP and GaAs were calculated from the secondary ion mass spectrometry atomic concentration depth profiles and were compared with TRIM92 values. Slight in-diffusion of sulfur was observed in both InP and GaAs at higher annealing temperatures for room temperature implants. Little or no redistribution of sulfur was observed for elevated temperature implants. Elevated temperature implants showed higher activations and higher mobilities compared to room temperature implants in both GaAs and InP after annealing. Higher peak electron concentrations were observed in sulfur-implanted InP (n ≈ 1 × 10¹⁹ cm⁻³) compared to GaAs (n ≈ 2 × 10¹⁸ cm⁻³). The doping profile for a buried n⁺ layer (n ≈ 3.5 × 10¹⁸ cm⁻³) of a positive-intrinsic-negative diode in GaAs was produced by using Si/S coimplantation.     

The temperature and pressure dependence of the electron and hole mobilities in GaxIn1-xAsyP1-y alloys

A wide range of samples of both n-type and p-type Ga_xIn_1-xAs_yP_1-y on InP has been grown by LPE with carrier concentrations in the low 10¹⁶cm⁻³range. The electron mobility (μ_e) at room temperature decreased from about 4000 cm²V⁻¹s⁻¹ at y = 0 and passed through a shallow minimum near y = 0.25. At high y values, μ_e rose steeply, reaching 11 000 cm²V⁻¹s⁻¹ at the ternary boundary. In the p-type material the hole mobility (μ_p) varied from 140 cm V⁻¹s⁻¹ in InP, passed through a minimum of about 70 cm²V⁻¹s⁻¹ near y = 0.5 and then increased swiftly towards the ternary boundary. The temperature dependence of both μ_e and μ_p suggested the presence of alloy or space-charge scattering. In order to distinguish between these two mechanisms the pressure coefficient of the direct band-gap dE_o/dP was measured as a function of y by observing the movement with pressure of the photoconductive edge. From dE_o/dP the pressure variation of the effective mass was deduced. By measuring the change in electron and hole mobilities with pressure, it was then possible to establish that alloy scattering rather than space-charge scattering was occurring. From the composition dependence of the alloy scattering potentials for electrons and holes predictions have been made of the variation of μ_e and μ_P with temperature, pressure and dopant Presently a Nuffield Science Fellow concentration. At room temperature a maximum electron mobility of about 11,200 cm²V⁻¹ s⁻¹ is indicated. Presently a Nuffield Science Fellow     

Research of SiO2/InP structure prepared by photo-CVD

The SiO₂ film as an insulator in InP MOS structure was grown by mercury-sensitized photo induced chemical-vapor deposition (photo-CVD) utilizing gaseous mixture of monosilane (SiH₄) and nitrous oxide (N₄O) under 253.7 nm ultraviolet light irradiation. The PHOTOX SiO₂ film (i.e., SiO₂ film prepared by photo-CVD system) deposited at 250° C has a refractive index of 1.46 and breakdown field strength of 7.0 MV/cm. The 1 MHz capacitance-voltage characteristics of the InP MOS diode was measured to study the interface state densities. The minimum value is 1.2 × 10¹¹ cm⁻²eV⁻¹ for the sample prepared at a substrate temperature of 250° C.     

STUDY OF THE ANODIZATION OF Al FILM ON InP SUBSTRATE AND ITS PROPERTIES

The anodization of Al film on InP substrate and properties of anodic Al_2O_33/InPhave been investigated by AES,DLTS,I-V,C-V and ellipsometer.The results show that theanodic oxide Al_2O_3 has a permittivity of 11～12 and a resistivity of 1.3×10~(13) ohm-cm.Interfacestate density at Al_2O_3/InP is about 10~(11) cm~(-2)·eV~(-1).DLTS reveals that there is a continuouslydistributed interface electron traps at Al_2O_3/InP interface.Anodic Al_2O_3 exhibits good stabilityand electrical properties and could be used for passivation,diffusion mask and gate insulator,etc.