Excellent Surface Morphology Research Articles

High Quality GaAs on Si by Selective Area Epitaxy

ABSTRACTSelective area Epitaxy (SE) of high quality GaAs on Si films has been achieved using conventional MOCVD and Atomic Layer Epitaxy (ALE) nucleation techniques. Epitaxial GaAs films were deposited inside windows etch patterned in the oxide coated Si wafers. SE was found to eliminate wafer warpage, reduce film cracking and reduce the tensile stresses for islands less than 200 µm/side. Complete stress relief has been achieved in 10 µm/side islands after oxide removal. Defect reduction techniques have been employed resulting in two orders of magnitude reduction in the dislocation density and excellent surface morphologies. This paper addresses the potential of SE, by the above techniques in improving the quality of the GaAs on Si films.

Growth and Characterization of Highly Oxygen-Doped GaAs

ABSTRACTHigh levels (≃ 1018cm-3) of oxygen were introduced into GaAs by using dimethyl aluminum methoxide (DMAlM0) as an oxygen-bearing precursor during metalorganic vapor phase epitaxy. Layers co-doped with oxygen and intentionally added silicon, both to concentrations of ≃ 1018 cm-3, were depleted of free carriers and had no measurable luminescence. Deep levels were present in layers grown with lower oxygen incorporation, but the compensation mechanism due to oxygen incorporation is not apparently tied to a specific defect level. The material with the electronic deep levels also possessed deep luminescence energy lines. All layers exhibited excellent surface morphology. For comparison, other layers were grown by introducing low levels of 02 and trimethyl aluminum during GaAs growth. The surface morphology of these layers was usually hazy and the layers did not exhibit the same well defined electrical and optical characteristics as the layers grown with DMAlMO.

Epitaxial Y-Ba-Cu-O thin films on MgO deposited by high-pressure reactive magnetron sputtering

Y-Ba-Cu-O thin films have been prepared on MgO(100) substrates by rf reactive magnetron sputtering from a single ceramic target. By adopting high total pressures, typically 280 mTorr, and relatively low substrate temperatures of approximately 650 °C, epitaxial films with the relations (001) YBa2Cu3Oy∥(001)MgO and [100]YBa2Cu3Oy∥[100]MgO can be reproducibly obtained. A high degree of epitaxy is confirmed by x-ray pole figure measurements and ion channeling. These films require a brief rapid thermal oxygen anneal at typically 850 °C, to exhibit sharp superconducting transitions with zero resistance around 75 K. Films deposited at higher temperatures above 700 °C show transitions as deposited with zero resistance near 80 K. The quality of the transition is correlated with expanded lattice constants with the best transitions occurring in films whose lattice constants approach that of the bulk. The films have high critical current densities of 1–5×106 A/cm2 at 4.2 K. They also show good uniformity and excellent surface morphology with a roughness less than 10 nm and can be readily patterned to micrometer and submicrometer dimensions.

MBE growth of high-quality GaAs

This paper reviews the requirements and current practices in the molecular-beam epitaxial (MBE) growth of high-quality GaAs. High-quality growth of GaAs means excellent control on the growth process leading to an excellent surface morphology, structural, electrical and optical properties of the deposited GaAs. Background material is presented about the MBE technique, the MBE system and its initial preparation for growth, molecular-beam source materials, substrate preparation and the growth conditions. The importance of meticulousness at every step is emphasized. Then, to illustrate that the MBE-GaAs has reached a level of perfection, experimental data are presented which show an excellent control on the growth rate and its lateral uniformity (±0.75%), the presence of very low level of background impurities (∼ low 10 13 cm -3) and high electron mobilities (μ peak ∼ 3 × 10 5 cm 2 V -1 s -1 at 42 K for n ∼ 3 × 10 13 cm -3). In addition, it is shown that MBE-GaAs is intrinsically free from electron and hole deep traps. Chemical impurities in the impure arsenic-source are shown to be the main limiting factors in determining the transport and optical properties and formation of deep centers in MBE-GaAs. Such chemical impurities may, however, originate from other sources as well.

Chemical preparation of GaSb(001) substrates prior to MBE

The chemical preparation of GaSb(001) substrates was performed by Br2-HCl-HNO3-CH3COOH solution. The removed layer thickness was evaluated as a function of the constituent concentrations and the etching time. The surface quality was controlled by SEM, RHEED and AES. With this treatment, excellent surface morphology of substrates and growth film is obtained.

High-Power AlGaAs/GaAs DH Stripe Laser Diodes on GaAs-on-Si Prepared by Migration-Enhanced Molecular Beam Epitaxy

We report on high-power low-threshold AlGaAs/GaAs double heterostructure (DH) stripe laser diodes on Si substrates by a hybrid growth of migration-enhanced molecular beam epitaxy (MEMBE) and metalorganic chemical vapor deposition (MOCVD). MEMBE-grown GaAs-on-Si had excellent surface morphology and showed much lower dislocation density than that of normal two-step MBE-grown or in situ annealed layers. The MEMBE growth and material characterization are described in detail. The 6-µm-wide oxide stripe lasers showed the highest peak power of up to 184 mW per facet reported to date, room-temperature pulsed threshold currents as low as 150 mA, and differential quantum efficiencies as high as 30% without mirror facet coating. The intrinsic threshold current density has been estimated to be about 2 kA/cm2 when taking current spreading and lateral diffusion effects into account. For comparison, the room-temperature pulsed threshold current density of 1.1 kA/cm2 was obtained for the broad-area DH laser diode fabricated on GaAs substrates in the same epitaxial deposition.

Thermal stability of tungsten ohmic contacts to the graded-gap InGaAs/GaAs/AlGaAs heterostructure

Nonalloyed tungsten ohmic contacts to the Inx Ga1−x As/GaAs/Aly Ga1−y As (x=0.4, y=0.25) graded-gap heterostructure showed excellent surface morphology after annealing of up to 1000 °C for 10 s. The minimum value for the specific contact resistance (1.3×10−6 Ω cm2 ) was obtained following annealing at 600 °C for 10 s. The increase in contact resistivity at higher temperatures was related to the increase in the heterostructure sheet resistance due to layer intermixing and In and Ga outdiffusion. The W/InGaAs graded-gap refractory ohmic contact can be used as a self-aligned emitter in heterojunction bipolar transistors.

Ultra-high throughput of GaAs and (AlGa)As layers grown by MBE with a specially designed MBE system

Ultra-high throughput MBE growth of very pure and extremely uniform GaAs and (AlGa)As layers with excellent surface morphology can be realized using a newly developed MBE system. High throughput can be achieved by the combination of the simultaneous growth of seven 2 inch or three 3 inch epiwafers and of the automatic growth operated continuously day and night, without accelerating growth rates. The surface defect density has been reduced to the allowable level even for GaAs microwave monolithic ICs. Hall mobilities 1 × 10 5 cm 2/V · s at 77 K were routinely obtained from slightly Si-doped GaAs layers. The microwave devices fabricated from the epiwafers grown by this system showed excellent performance.

Organometallic chemical vapor deposition of epitaxial ZnGeP 2 films on (001) GaP substrates

In this paper, the organometallic chemical vapor deposition of epitaxial layers of the II-IV-V 2 semiconductor ZnGeP 2 and its alloys with Ge on (001) GaP substrates is reported. Mirror smooth epitaxial surface morphology is obtained at Zn(CH 3) 2 to GeH 4 flow rate ratios larger than 1:3. In the range of Zn(CH 3) 2 and PH 3 flow rates studied, the growth rate is determined by the flow rate of GeH 4. Secondary ion mass spectra, X-ray diffraction, and transmission electron microscopy have been utilized for the characterization of these thin films and correlated to the growth conditions. Also, bulk single crystals of ZnGeP 2 have been grown from the melt to provide a standard for comparison with the epitaxial layers. Generally, the epitaxial films are purer than the bulk single crystals. Solid solutions (ZnGeP 2) 1- x Ge x can be grown with excellent surface morphology in the range x < 0.1, and transmission electron microscopy indicates that the chalcopyrite structure film is of higher microstructural perfection than the zinc blende structure alloy films.

ZnGeP2: A Wide Bandgap Chalcopyrite Structure Semiconductor for Nonlinear Optical Applications

ABSTRACTIn this paper we report the growth and characterization of wide bandgap chalcopyrite structure semiconductor ZnGeP2 epitaxial layers by open tube MOCVD and ZnGeP2 single crystals by high-pressure vapor transport (HPVT). The electrical and optical properties of these crystals have been investigated by Hall measurements, absorption spectroscopy, photoconductivity and photoluminescence spectroscopy. The onset of the absorption edge for HPVT ZnGeP2 at 1.99 eV is in accord with the pseudodirect bandgap of this material. Both the meltgrown crystals and epitaxial layers show extended band tailing in the transparency range of ZnGeP2 depending on the growth conditions. Recently we have shown that epitaxial ZnGeP2 films can be grown with excellent surface morphology by MOCVD on (111) GaP substrates. These films should be suitable for phase matched second harmonic generation utilizing CO laser radiation in thick film heterostructures.

A Study of the In Situ Epitaxial Growth of the 123 Ybco Films from a Stoichiometric Target by Rf Magnetron Sputtering

AbstractThe synthesis parameters have been systematically examined for the in situ growth of high temperature superconducting Y‐Ba‐Cu‐0 thin films from a stoichiometric target by rf magnetron sputtering. By properly adjusting the deposition temperature, the total sputtering (O2+Ar)‐pressure and the O2‐partial pressure, we have reproducibly obtained 123 YBCO films with a zero resistivity temperature Tcz = 84 K and a transition width of 3 K°. The films so obtained have excellent surface morphology and a surface roughness better than ∼ 5 nm.

Mocvd Growth of CdTe and HgTe on GaAs in a Vertical, High-Speed, Rotating-Disc Reactor

AbstractThe metalorganic chemical vapor deposition (MOCVD) growth of CdTe and HgTe on GaAs (111) and (100) substrates in a vertical, high-speed, rotating-disc reactor was investigated. A range of total reactor pressure, carrier gas flow rate, chemical concentrations, deposition temperature, and rotation rate have been investigated in an attempt to optimize growth conditions. Diisopropyltelluride (DIPTe) and Dimethylcadmium (DMCd) were used as growth precursors. Thickness uniformity varies less than +/- 1.5% over 50 mm diameter wafers. Films having FWHM X-ray rocking curves less than 90 arcsec were obtained on GaAs (111) substrates. The films have excellent surface morphology, exhibiting less than 5x104 cm-2 orange peel dents which are &lt;&lt; 1 µm in size. An elemental mercury source was added to the growth system. Initial results for the growth of HgTe and HgCdTe will be discussed in this text.

Growth and characterization of GaAs layers on Si substrates by migration-enhanced molecular beam epitaxy

We first report on migration-enhanced molecular beam epitaxial (MEMBE) growth and characterization of the GaAs layer on Si substrates (GaAs/Si). Excellent surface morphology GaAs layers were successfully grown on (100)Si substrates misoriented 4° toward the [110] direction. The MEMBE growth method is described, and material properties are compared with those of normal two-step MBE-grown or in situ annealed layers. Micrographs of cross-section view transmission electron microscopy (TEM) and scanning surface electron microscopy (SEM) of MEMBE-grown GaAs/Si showed dislocation densities of 1×107 cm−2, over ten times lower than those of normal two-step MBE-grown or in situ annealed layers. AlGaAs/GaAs double heterostructures have been successfully grown on MEMBE GaAs/Si by both metalorganic chemical vapor deposition and liquid phase epitaxy.

AuGeNi ohmic contacts to n-InP for FET applications

AuGeNi ohmic contact formation on Si-implanted InP has been investigated. Ohmic contacts suitable for application to field-effect transistors are obtained at alloying temperatures between 360°C and 630°C, with contact resistance around 0.02–0.07 μ · mm. A liquid phase appears at an alloying temperature of about 460°C. in consequence, contacts with excellent surface morphology and edge definition are obtained for alloying temperatures between 360°C and 460°C. Four different regimes in the alloying temperature behavior of the AuGeNi/InP system are observed and their physical origin is discussed. A close to quadratic correlation exists between the achieved contact resistance and the underlying semiconductor sheet resistance.

Kinetics of molecular‐beam epitaxial HgCdTe growth

The surface kinetics that govern molecular‐beam epitaxial (MBE) growth of HgCdTe films places strict boundaries on the optimal deposition conditions to be selected. This paper will examine the limits imposed by the surface kinetics on the Hg flux, substrate orientation, and substrate temperature to be chosen for MBE HgCdTe film growth. The range of Hg flux available to grow single crystalline HgCdTe (as determined by reflection high‐energy electron diffraction) will be seen to vary significantly with the (112)Te, (112)Cd, and (001) growth orientations. The HgCdTe(112)Te films are deposited with a high Hg condensation coefficient at 200 °C (0.04–0.10), have an excellent surface morphology, and avoid the cellular twins that are found in HgCdTe(111)Te layers. However, each of the three orientations result in faceted growth at substrate temperatures near 200 °C; at this substrate temperature, HgTe begins to desorb from the growth surface which leads to a preferential exposure of the lower energy (111) planes....

A high-performance InGaAs/InAlAs double-heterojunction bipolar transistor with nonalloyed n/sup +/-InAs cap layer on InP(n) grown by molecular beam epitaxy

An InGaAs/InAlAs double-heterojunction bipolar transistor (DHBT) on InP(n) grown by molecular-beam epitaxy (MBE) that exhibits high DC performance is discussed. An n/sup +/-InAs emitter cap layer was used for nonalloyed contacts in the structure and specific contact resistances of 1.8*10/sup -7/ and 6.0*10/sup -6/ Omega -cm/sup 2/ were measured for the nonalloyed emitter and base contacts, respectively. Since no high-temperature annealing is necessary, excellent contact surface morphology on thinner base devices can easily be obtained. In devices with 50*50- mu m/sup 2/ emitter area, common-emitter current gains as high as 1500 were achieved at a collector current density of 2.7*10/sup 3/ A/cm/sup 2/. The current gain increased up to 2000 for alloyed devices. >

Ultra-High Throughput of GaAs and (AlGa)As Layers Grown by Molecular Beam Epitaxy (MBE) with a Specially Designed MBE System

The ultra-high throughput of extremely uniform GaAs and (AlGa)As layers with excellent surface morphology can be realized by MBE with a new MBE system designed for both a drastic increase of the throughput and a reduction of the surface defect density. The simultaneous growth of seven 5-cm-dia. epiwafers can be achieved with a thickness variation of less than 2% by optimizing the effusion cell geometry. A computer-controlled growth sequencer and a newly developed source recharging system are incorporated for automatic growth, and operated continuously day and night without venting the growth chamber even during source recharging. The surface defect density has been reduced to less than 50/cm2 by the introduction of a modified Ga cell and a face-down sample-transfer system. This system allows the growth of nearly 100 GaAs FET or HEMT wafers each day (24 hr). The devices constructed from these wafters showed excellent performance.

Low-temperature preparation of high T c superconducting thin films

Thin superconducting films of Y-Ba-Cu-O were prepared at 650 °C using the pulsed laser deposition technique. The as-deposited films were fully superconducting at low temperature (30 K). After annealing in oxygen at 450 °C for 3 h, the films exhibited superconductivity with zero resistance at temperatures as high as 83 K. Film-substrate interface reaction was minimal as revealed by Rutherford backscattering and Auger electron spectrometry. These films processed at such low temperatures are also found to have excellent planar surface morphology and high critical current density.

Organometallic vapor phase epitaxial growth of a new semiconductor alloy: GaP1−xSbx

The III/V semiconductor alloy GaP1−xSbx has been grown for the first time. This alloy, which has a large miscibility gap at the growth temperatures of 530–600 °C, has been grown by organometallic vapor phase epitaxy at atmospheric pressure. In spite of the miscibility gap, which is calculated to extend from x=0.01 to 0.99 at 530 °C, layers with excellent surface morphologies could be grown throughout the entire composition range. The 10 K energy band gap has been determined as a function of composition by using photoluminescence, x-ray diffraction, and electron microprobe analysis, yielding bowing parameters of 3.8 and 2.7 eV for the Γ and X conduction band minima, respectively.

Migration-Enhanced Molecular Beam Epitaxial Growth and Characterization of GaAs on Si Substrates

ABSTRACTWe first report on migration-enhanced molecular beam epitaxial (MEMBE) growth and characterization of the GaAs layers on Si substrates (GaAs/Si). Excellent surface morphology GaAs layers were successfully grown on (100) Sisubstrates misoriented 4 toward [110] direction. The MEMBE growth method isdescribed and material properties are compared with those of normal two-step MBE-grown or in-situ annealed layers. Micrographs of cross-sectional view transmission electron microscopy (TEM) and scanning surface electron microscopy (SEM) of MEMBE-grown GaAs/Si showed dislocation densities of 107 cm-2 over ten times lower than those of two-step MBE-grown or in-situ annealedlayers. AlGaAs/GaAs double heterostructure lasers and light-emitting diodeshave been successfully grown on MEMBE GaAs/Si by both metal organic chemical vapor deposition and liquid phase epitaxy. MOCVD-grown lasers showed peak output power as high as 184 mW/facet, pulsed threshold currents as low as150 mA at 300 K, and differential quantum efficiencies of up to 30 %. The LPE-grown light-emitting diodes showed output powers of 1.5 mW and external quantum efficiencies of 3.3 mW/A per facet.