Source Si Molecular Beam Epitaxy Research Articles

Influence of phosphine flow rate on Si growth rate in gas source molecular beam epitaxy

As reported by other authors, we have also observed that the Si growth rate decreases with increasing phosphine (PH 3) flow rate in gas source Si molecular beam epitaxy using phosphorous (P) as a n-type dopant. Why small quantity PH 3 can affect Si growth rate? Up to now, the quantitative characterization of PH 3 flow influence on Si growth rate is little known. In this letter, the PH 3 influence will be analyzed in detail and a model considering strong P surface segregation and its absorption of hydrogen will be proposed to characterize the effect.

Growth of vertical cavity on buried-oxide substrate by gas-source Si molecular-beam epitaxy and coupled mode luminescence of strained Si1−xGex/Si quantum wells

Successful growth of a new class of Si-based vertical cavity structure is demonstrated using a buried-oxide substrate [separation-by-implantation-oxygen (SIMOX)] by gas source Si molecular beam epitaxy. The cavity is terminated with the Si/buried-oxide and top Si/air interface mirrors. Integration of strained Si1−xGex/Si quantum wells in the vertical cavity lead to the observation of spectral coupling of luminescence to the cavity longitudinal modes. Clear oscillations were observed in reflectance and photoluminescence excitation spectra.

Spectral modulation of luminescence of strained Si1−xGex/Si quantum wells in a vertical cavity with air/Si and Si/SiO2 interface mirrors

Integration of strained Si1−xGex/Si quantum wells (QWs) in a vertical cavity is demonstrated on a Si substrate with a buried-oxide using gas source Si molecular beam epitaxy. Spontaneous emission from the SiGe QW is found to be spectrally coupled to the longitudinal modes of a vertical cavity with buried oxide/Si and top Si/air interface mirrors, which is in excellent agreement with separate reflectance measurements. In addition, clear oscillations were observed in photoluminescence excitation spectra for photon energies even above the Si band gap, demonstrating cavity modulation of the incident light absorption.

Abrupt Si/Ge interface formation using atomic hydrogen in Si molecular beam epitaxy

Compositional abruptness of strained Si/Ge heterointerfaces grown by solid source Si molecular beam epitaxy under supply of atomic hydrogen (AH) was investigated using secondary ion mass spectrometry and reflection high-energy electron diffraction. Systematic variation of growth temperature and AH exposure pressure revealed that Ge segregation length is a steadily decreasing function of AH coverage on the growth surface.

Room temperature photoluminescence in strained Si1−xGex/Si quantum wells

Photoluminescence (PL) observation at room temperature is reported in strained Si1−xGex/Si multiple quantum wells (MQWs) grown by gas source Si molecular beam epitaxy. It was found that QW PL is enhanced when MQWs are arranged so that photogenerated carriers are trapped efficiently to QWs without significant loss. This was achieved by locating MQWs over the penetration depth of the excitation light. QW PL was found to develop with a power exponent of 1.8 for lower excitation. QW PL was observed at room temperature for MQW samples with x up to 0.69.

Self-modulating Sb incorporation in Si/SiGe superlattices during molecular beam epitaxial growth

Self-modulating incorporation of Sb atoms has been found in Si/SiGe superlattices grown by conventional solid source Si molecular beam epitaxy. The origin of this phenomenon has been attributed to the difference in the segregation length of Sb atoms in Si and SiGe layers. It has been found that the segregation length of Sb in Si 1− x Ge x layers increases as the Ge composition, x, increases and that Sb atoms are incorporated mainly in Si layers when Si/SiGe superlattices are grown.

High-temperature operation of strained Si0.65Ge0.35/Si(111) p-type multiple-quantum-well light-emitting diode grown by solid source Si molecular-beam epitaxy

Electroluminescence (EL) was observed at temperatures up to 60 °C in p-type strained Si0.65Ge0.35/Si multiple-quantum-well (MQW) diode structures grown on Si(111) substrates by Si molecular-beam epitaxy. No-phonon line and its transverse optical phonon replica were well-resolved in the room-temperature EL spectrum for the first time. EL spectrum was dominated by a broad alloy band located below the band-edge state by ≊100 meV at lower temperatures, which was taken over by clear band-edge emissions at elevated temperatures. The emission intensity of the alloy band exhibited a saturation behavior with increasing injection current while the band-edge emission was found to develop with a power exponent of 1.4.

Observation of deep-level-free band edge luminescence and quantum confinement in strained Si1−xGex/Si single quantum well structures grown by solid source Si molecular beam epitaxy

Well-resolved band edge luminescence with no deep level emissions is reported for Si0.8Ge0.2/Si single quantum well (SQW) structures grown at high substrate temperatures (Ts≊620 °C) by solid source Si molecular beam epitaxy (MBE). No-phonon (NP) transitions due to symmetry-breaking alloy disordering in SiGe layers and transverse optical (TO) phonon replicas were clearly identified. With decreasing well width, NP and TO emissions were found to show systematic blue shift due to quantum confinement effect. Excellent crystal quality was evidenced by total absence of defect-related deep level emissions characteristic of photoluminescence spectra of samples grown at lower temperatures, Ts<600 °C. This result indicates that high growth temperature environment is essential to efficient radiative recombination in SiGe/Si QW structures.

Intensity oscillations in reflection high-energy electron diffraction during disilane gas source molecular beam epitaxy

Reflection high-energy electron diffraction (RHEED) intensity oscillations during growth in disilane gas source Si molecular beam epitaxy (MBE) on Si(100) and (111) surfaces were observed under low substrate temperature and high disilane flow rate conditions. As has been observed in solid source Si MBE, these oscillations included periods corresponding to periods for monolayer and bilayer growth. On Si(100) surfaces, growth rate, which was estimated from the periods of the oscillations, was limited by a reaction process whose activation energy was 47 kcal/mol. This rate limitation is thought to stem from hydrogen desorption from monohydride phase on the Si(100). On Si(111) surfaces, oscillations in specular beam intensity were clearly observed. Although clear oscillations in the 7×7 diffraction spots could not be observed because of intensity weakness of the fractional order spots under disilane exposure. At high disilane flow rates, 7×7 diffraction spots almost disappeared and only fundamental spots were observed. The fundamental 1×1 RHEED pattern also indicated monohydride structure on Si(111) surface during the growth.

B doping using B2H6 in gas source Si molecular beam epitaxy

A new gas mixing system was devised for the control of a gaseous dopant during gas source Si molecular beam epitaxy. The performance of this gas mixing system was demonstrated using B2H6 gas dopant for B doping. B doping level control over five decades was successfully achieved. The B-doping concentration was found to be proportional to the B2H6/Si2H6 flow rate ratio. This relationship holds in both the supply-controlled and the reaction-controlled growth regions. This result indicates that B2H6 is incorporated into epitaxial layers by a similar dissociative adsorption mechanism on Si2H6.

Gas source molecular-beam epitaxy of Si and SiGe using Si2H6 and GeH4

Gas source molecular-beam epitaxy (MBE) has been studied as a low-temperature Si and SiGe epitaxial method. Specular single-crystalline silicon films were successfully grown by the gas source Si MBE technique at a substrate temperature of about 650 °C. N-type doping was carried out using PH3 gas as a dopant and the maximum electron concentration of 2.9x1019cm−3 was obtained. Furthermore, p-type doping using B2H6 gas was carried out for the first time and the maximum hole concentration of 9.5×1017cm−3 was successfully achieved. The SiGe alloy layer was also grown by the gas source MBE technique using GeH4 as a Ge source gas. The Ge concentration of the sample could be precisely controlled by the molar fraction of Ge in supply and it was increased up to 0.30 with increasing the gas ratio of GeH4 to Si2H6.

Heterojunction bipolar transistor fabrication using Si1−xGex selective epitaxial growth by gas source silicon molecular beam epitaxy

B doping in Si1−xGex was successfully achieved using HBO2 cell in gas source Si molecular beam epitaxy (Si-MBE). Combining this B doping method and selective epitaxial growth of Si1−xGex by gas source Si-MBE, B-doped Si1−xGex selective epitaxial growth was found to be possible. This B-doped Si1−xGex selective epitaxial growth was applied to Si1−xGex/Si heterojunction diode and Si1−xGex base heterojunction bipolar transistor (HBT) fabrications. The Si1−xGex base HBT (x=0.16, 0.22, 0.31) showed higher hFE in as-grown condition than that for a homojunction transistor. The band-gap difference between the Si1−xGex base and the Si emitter was estimated by the temperature dependence of the collector current ratio between the HBT and the homojunction transistor.

Gas Source Si-Mbe

ABSTRACTGas source Si molecular beam epitaxy (Si-MBE) apparatus has been devised. The growth mechanism was studied using reflection high energy electron diffraction (RHEED) intensity oscillation. Si epitaxial layers grew through a dissociative adsorption of Si2H6 molecules on Si surfaces. This dissociative adsorption enables a selective epitaxial growth on SiO2 patterned Si wafers. At low temperatures, the growth rate was limited by a desorption of hydrogen which terminates surface dangling bonds. Doping with B, Sb and P were also studied. B doping was achieved using HBO2 Knudsen cell or B2H6 gas dopant. Sb doping used an ionized doping cell. P doping was achieved using PH3 gas dopant. The effect of B doping on the growth was studied using RHEED oscillation. A doped layer's selective epiataxial growth was possible by selective epitaxial growth under doping. This technique was applied to bipolar transistor fabrication. Moreover, using GeH4, Si1−xGex compound growth and its selective epitaxial growth was achieved. Using this Si1−xGex selectively grown layer, a Si1−xGex base heterobipolar transistor (HBT) was also fabricated. An electron cyclotron resonance (ECR) gas source Si-MBE cell was used for a low temperature surface cleaning and a surface termination by atomic hydrogen.

Si (111) surface cleaning using atomic hydrogen and SiH2 studied using reflection high-energy electron diffraction

The Si(111) wafer covered by a thin protective oxide layer was cleaned in disilane gas source Si molecular-beam epitaxy chamber. The effect of the electron cyclotron resonance (ECR) cracked/uncracked disilane or hydrogen irradiation on the initial surface cleaning was studied by observing the reflection high-energy electron diffraction pattern change. The ECR-cracked disilane irradiation was the most effective for lowering the cleaning temperature and the surface cleaning was achieved at 680 °C. The uncracked disilane and the ECR-cracked hydrogen irradiation were also effective for lowering the cleaning temperature. The uncracked hydrogen irradiation has no effect for lowering the cleaning temperature. The SiH2 and H were main species of the ECR-cracked disilane and these played important roles in the cleaning process.

High doping of phosphorus in Si using gas source molecular beam epitaxy

Phosphorus doping using PH3 in gas source Si molecular beam epitaxy was studied. High phosphorus doping up to 2×1020 cm−3 was successfully achieved. The phosphorus concentration in the epitaxial layer was proportional to the PH3 flow rate. Moreover, selective growth of the phosphorus-doped layer was possible. The p-n diode, which consisted of a selectively grown phosphorus-doped layer, a p−-Si (100) substrate, and a SiO2 sidewall, showed a normal I-V characteristic.

Hydrogen passivation effect in Si molecular beam epitaxy

Hydrogen passivation of the clean Si(100) surface to prevent growth of native oxides after air exposure was studied by supplying atomic hydrogen at several temperatures between room temperature and 650 °C. Atomic hydrogen was generated with high efficiency by the electron cyclotron resonance plasma cell of the gas source Si molecular beam epitaxy apparatus. The passivation effect was examined by observing the oxygen KLL Auger peak height of the passivated wafer after 12 h air exposure. The wafer supplied with atomic hydrogen at temperatures below 400 °C showed an obvious passivation effect, while the wafer supplied with hydrogen at temperatures above 400 °C showed no passivation effects. The solid source Si MBE growth was done on these hydrogen-passivated and 12 h air-exposed wafers at the growth temperature of 600 °C without any initial surface cleaning process. A good crystal quality film which showed a sharp 2×1 reflection high-energy electron diffraction pattern was obtained on the wafer supplied with hydrogen at temperature below 400 °C.