Evaluation of magnesium and manganese as the P-type dopant for InP/InGaAs heterojunction transistors

Among Zn, Cd, Mg, Mn, and Be as the p-type dopant in InGaAs, Mg and Mn were taken as candidates for the dopant in the base region of InP/InGaAs heterojunction transistors. Properties of the two dopants were investigated in terms of doping reproducibility, diffusion in solid phase, and attainable optical gain in the InP/InGaAs heterojunction phototransistors. Mn was found to be suitable for the p-type dopant in the InGaAs base region of InP/InGaAs n-p⁺-n transistors.     

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.     

A comparison of TMGa and TEGa for low-temperature metalorganic chemical vapor deposition growth of CCI4-doped inGaAs

Factors which influence the alloy composition and doping level of CCl₄-doped In_0.53Ga_04.7As grown at low temperatures (450°C < T_g < 560°C) by low-pressure metalorganic chemical vapor deposition (MOCVD) have been investigated. The composition is highly dependent on substrate temperature due to the preferential etching of In from the surface during growth and the temperature-dependent growth efficiency associated with the Ga source. The lower pyrolysis temperature of TEGa relative to TMGa allows the growth of CCl₄-doped InGaAs at lower growth temperatures than can be achieved using TMGa, and results in improved uniformity. High p-type doping (p ∼ 7 × 10¹⁹ cm^-8) has been achieved in C-doped InGaAs grown at T = 450°C. Secondary ion mass spectrometry analysis of a Cdoping spike in InGaAs before and after annealing at ∼670°C suggests that the diffusivity of C is significantly lower than for Zn in InGaAs. The hole mobilities and electron diffusion lengths in p⁺-InGaAs doped with C are also found to be comparable to those for Be and Zn-doped InGaAs, although it is also found that layers which are highly passivated by hydrogen suffer a degradation in hole mobility. InP/InGaAs heterojunction bipolar transistors (HBTs) with a C-doped base exhibit high-frequency performance (f_t = 62 GHz, f_max=42 GHz) comparable to the best reported results for MOCVD-grown InP-based HBTs. These results demonstrate that in spite of the drawbacks related to compositional nonuniformity and hydrogen passivation in CCl₄-doped InGaAs grown by MOCVD, the use of C as a stable p-type dopant and as an alternative to Be and Zn in InP/ InGaAs HBTs appears promising.     

Optimization of the base electrode for InGaAs/InP DHBT structures with a buried emitter-base junction

We have optimized the base electrode for InGaAs/InP based double heterojunction bipolar transistors with a buried emitter-base junction. For the buried emitter-base structure, the base metal is diffused through a thin graded quaternary region, which is doped lightly n-type, to make ohmic contact to the p⁺InGaAs base region. The metal diffusion depth must be controlled, or contact will also be made to the collector region. Several metal schemes were evaluated. An alloy of Pd/Pt/Au was the best choice for the base metal, since it had the lowest contact resistance and a sufficient diffusion depth after annealing. The Pd diffusion depth was easily controlled by limiting the thickness to 50?, and using ample Pt, at least 350?, as a barrier metal to the top layer of Au. Devices with a 500? base region show no degradation in dc characteristics after operation at an emitter current density of 90 kA/cm² and a collector bias, V_CE, of 2V at room temperature for over 500 h. Typical common emitter current gain was 120. An f_t of 95 GHz and f_max, of 131 GHz were achieved for 2×4 μm² emitter size devices.     

Zn doping of InP, InAsP/InP, and InAsP/InGaAs heterostructures through metalorganic vapor phase diffusion (MOVPD)

Zinc incorporation by post-growth metalorganic vapor phase diffusion (MOVPD) is used to achieve high p-doping, which is desirable for the fabrication of photodiodes. Diethylzinc (DEZ) is used as precursor and Zn is diffused into InP and InAs_0.6P epitaxial layers grown by low pressure metalorganic vapor phase epitaxy (MOVPE) on different substrate orientations, enabling the investigation of the dislocation density on the Zn incorporation. Diffusion depths are measured using cleave-and-stain techniques, resistivity measurements, electrochemical profiling, and secondary ion mass spectroscopy. High hole concentrations of, respectively, 1.7 10¹⁹ and 6 10¹⁸ cm⁻³, are obtained for, respectively, InAs_0.60P and InP. The diffusion coefficients are derived and the Zn diffusion is used for the fabrication of lattice-mismatched planar PIN InAsP/InGaAs photodiodes.     

High speed non-selfaligned InP/InGaAs Npn heterojunction bipolar transistor grown by low pressure metal organic vapour phase epitaxy

Lattice matched GaInAs/InP Npn heterojunction bipolar transistors (HBTs) have been grown by lower pressure metal organic vapour phase epitaxy (MOVPE) and precessed with non-selfaligned fabrication techniques. The transistors exhibit a cutoff frequency of 60 GHz and maximum oscillation frequency of 32 GHz which are the highest values reported to date for GaInAs/InP HBTs grown by MOVPE.<>     

InP/InGaAs double heterostructure bipolar transistors grown by MBE

Double heterostructure bipolar transistors have been fabricated on InP/InGaAs MBE material. Current gains of up to 80 have been observed in the emitter-up configuration. The devices were fabricated using two diffusion techniques and selective etching to contact the base.     

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.     

InGaAs/lnP heterojunction bipolar transistor grown by all-solidsource molecular beam epitaxy

State-of-the-art InGaAs/InP heterojunction bipolar transistors were grown by all-solid source molecular beam epitaxy. Fabricated transistors showed cutoff frequencies of >100 GHz with an emitter area of 1.5×5 μm². Together with recent studies. These results demonstrate that the valved cracker technique is a very competitive nontoxic growth method     

Zinc-doping of InP during chemical beam epitaxy using diethylzinc

Diethylzinc was used as ap-type dopant source during InP growth by chemical beam epitaxy. In InP, electrically activated Zn saturated at a concentration of ∼2.0 × 10¹⁸ cm⁻³ for epilayers grown at 540‡ C. Higher role concentrations were obtained by lowering the growth temperature. However, measurements with SIMS indicated that very serious Zn diffusion occurred when the Zn concentration appeared to reduce the pyrolysis efficiency of trimethylindium. This caused a reduction in the InP growth rate and InAs mole fraction in InGaAs epilayers. No Zn “memory effect≓ was detected in our system. Undoped InP epilayers maintained an n-type background of ∼5 × 10¹⁵ cm⁻³.     

InP/InGaAs double-heterojunction bipolar transistors grown on (100)Si by metalorganic chemical vapor deposition

The authors report the successful fabrication of InP/InGaAs double-heterojunction bipolar transistors (DHBTs) grown by metalorganic chemical vapor deposition (MOCVD) on Si substrates. The Si substrates used were p-type (boron doped) FZ grown wafers with a resistivity of 5000 Ω×cm, oriented 2° off the (100) plane toward the [110] direction. Epitaxial layers for DHBTs were grown on the Si substrate with a thin GaAs buffer layer. A two-step growth process was applied for the InP layers on GaAs-on-Si wafers. The transistors exhibit high current gains over 200, which is comparable to those in transistors grown on InP substrates. The dislocations are found to increase the recombination current very little in the neutral base region, but increase in generation-recombination current at the emitter-base interface     

InGaAs/InP heterobipolar transistors for integration on semi-insulating InP substrates

InGaAs/InP npn heterojunction bipolar transistors (HBTs) have been fabricated from LPE layers grown on semi-insulating InP substrates for application to integrated circuits. The inverted emitter configuration is used, which allows the growth of the active layers without any additional steps. The HBTs show stable characteristics without any hysteresis and with current gains up to 25 for 0.7 ?m base width. To our knowledge this is the first report of InGaAs/InP HBTs on a semi-insulating substrate.     

InP/InGaAs(P)材料中的低温开管Zn扩散

为了在InP/InGaAs(P)材料中进行精确的选择扩散,同时又要保证外延生长的多层异质结构不被破坏,提出了一种新的低温开管Zn扩散方法。该法直至在T=500℃,t=5min的条件下,重复性仍很好。应用该法研究了低温条件下Zn在InP,InGaAs(P)材料中的扩散行为。实验首次发现,Zn在InGaAsP材料中的扩散速率与材料中P含量的平方成正比。     

Fabrication of high-speed InP/InGaAs/InP DHBT with a new self-aligned metallization technique for reduced base resistance

A new self-aligned emitter–base metallization (SAEBM) technique with wet etch is developed for high-speed heterojunction bipolar transistors (HBTs) by reducing extrinsic base resistance. After mesa etch of the base layer using a photo-resist mask, the base and emitter metals are evaporated simultaneously to reduce the emitter–base gap (S_EB) and base gap resistance (R_GAP). The InP/InGaAs/InP double heterojunction bipolar transistor (DHBT) fabricated using the technique has a reduced R_GAP, from 16.48 Ω to 4.62 Ω comparing with the DHBT fabricated by conventional self-aligned base metallization (SABM) process. Furthermore, we adopt a novel collector undercut technique using selective etching nature of InP and InGaAs to reduce collector–base capacitance (C_CB). Due to the reduced R_GAP, the maximum oscillation frequency (f_max) for a 0.5 μm-emitter HBT is improved from 205 GHz to 295 GHz, while the cutoff frequency (f_T) is maintained at around 300 GHz.     

Millimetre-wave InP/InGaAs heterojunction bipolar transistors witha subpicosecond extrinsic delay time

We report the microwave characteristics of InP/InGaAs heterojunction bipolar transistors (HBTs) using a carbon-doped base grown by chemical beam epitaxy (CBE). An extrinsic delay time of 0.856 ps was achieved by nonequilibrium transport in a very thin base layer and extremely small emitter parasitic resistance through the use of silicon δ-doping in the emitter ohmic contact layer. To our knowledge, this is the shortest extrinsic delay time of any bipolar transistors reported. This result indicates the great potential of InP/InGaAs HBTs for applications requiring a very large bandwidth     

Self-organization phenomenon of strained InGaAs on InP (311) substrates grown by metalorganic vapor phase epitaxy

We have demonstrated that a self-organization phenomenon occurs in strained InGaAs system on InP (311) substrates grown by metalorganic vapor phase epitaxy. This suggests that a similar formation process of nanocrystals exists not only on the GaAs (311)B substrate but also on the InP (311)B substrate. However, the ordering and the size homogeneity of the self-organized nanocrystals are slightly worse than those of the InGaAs/AlGaAs system on the GaAs (311)B substrate. The tensilely strained condition of a InGaAs/InP system with growth interruption in a PH₃ atmosphere reveals a surface morphology with nanocrystals even on the InP (100) substrate. It was found that strain energy and high growth temperature are important factors for self-organization on III-V compound semiconductors. Preliminary results indicate that the self-organized nanostructures in strained InGaAs/InP systems on InP substrates exhibit room temperature photoluminescent emissions at a wavelength of around 1.3 p.m.     

Zinc diffusion in InAsP/InGaAs heterostructures

A systematic study of the sealed ampoule diffusion of zinc into epitaxially grown InP, In_0.53Ga_0.47As, In_0.70Ga_0.30As, In_0.82Ga_0.18As, and through the InAsP/InGaAs interface is presented. Diffusion depths were measured using cleave-and-stain techniques, electrochemical profiling, and secondary ion mass spectroscopy. The diffusion coefficients, , were derived. For InP, D₀=4.82 × 10⁻²cm²/sec and E_a=1.63 eV and for In_0.53Ga_0.47As, D₀=2.02 × 10⁴cm²/sec and E_a=2.63 eV. Diffusion into the heteroepitaxial structures used in the fabrication of planar PIN photodiodes is dominated by the effects of the InP/InGaAs interface.     

Pd/Zn/Pd/Au ohmic contacts to ρ-Type InP

Low resistance ohmic contacts (ρ_c = 7 x 10^-5 Ω-cm ² ) have been fabricated to Zn-doped p-type InP using an annealed Pd/Zn/Pd/Au metallization. Palladium reacts with InP at low temperatures to form a Pd₂InP ternary phase, which is initially amorphous but crystallizes and grows epitaxially on InP. Zinc reacts with some of the overlying Pd to form PdZn (≅250° C), which decomposes at 400-425° C to form PdP₂, freeing up Zn to diffuse into Au as well as InP. The contact resistance reaches a minimum as the decomposition reaction takes place. The resultant ohmic contact is laterally uniform and consists of epitaxial Pd₂InP adjacent to InP, followed by a thin layer of PdP₂ and then the outer Au layer. Further annealing leads to a breakdown of the contact structure,i.e. decomposition of Pd₂InP, and an increase in contact resistance.     

InP/InGaAs HBTs with n+-InP contacting layers grown byMOMBE using SiBr4

InP/InGaAs heterojunction bipolar transistors (HBTs) with low resistance, nonalloyed TiPtAu contacts on n⁺-InP emitter and collector contacting layers have been demonstrated with excellent DC characteristics. A specific contact resistance of 5.42×10^-8 Ω·cm², which, to the best of our knowledge, is the lowest reported for TiPtAu on n-InP, has been measured on InP doped n=6.0×10¹⁹ cm^-3 using SiBr₄. This low contact resistance makes TiPtAu contacts on n-InP viable for InP/InGaAs HBTs