Two-step Epitaxy Research Articles

High-power broad-area buried-mesa lasers

Broad area lasers emitting near 940 nm are fabricated using a process based on two-step epitaxy. The n-side of the layer structure and the active layer are grown during the first epitaxial step, the p-side during the second. Between the first and the second step a shallow etching is used to remove the active layer from the two sides and at the two facets. This simple approach allows the creation of buried mesa lasers with non-absorbing mirrors, resulting in a reduced lateral current leakage, lower threshold current and higher efficiency, plus an increased robustness with respect to catastrophic optical damage.

Remarkable Strength Characteristics of Defect-Free SiGe/Si Heterostructures Obtained by Ge Condensation

We compare the morphological and structural features of SiGe membranes fabricated by three different processes: direct deposition of Si0.5Ge0.5 on Si(001) nominal substrate, direct deposition of Si0.5Ge0.5 on silicon on insulator, and deposition of SiGe with low Ge concentration on silicon on insulator followed by Ge enrichment by condensation. We show that the formation of fully strained Ge-rich layers free of defects with a flat surface is possible only by the two-step epitaxy–condensation process. We demonstrate that the condensation-based process enables the total inhibition of the morphological instability, together with the hindering of dislocations for critical thickness much greater than those commonly obtained by direct deposition. Those behaviors could be explained by the injection of self-interstitials in the Ge-rich layers during condensation. Such remarkable properties could be generalized to many other systems using a similar condensation process.

Process Control of Buried Layer Epitaxy by Barrel Type Furnace

Though the quality of epitaxial wafer prepared by barrel type epitaxial furnace is inferior to that by traditional single wafer furnace, it has a series of advantages such as high yield and low cost. The key issues and difficulties of the epitaxy process for buried layers IC wafers prepared by barrel type epitaxial furnace were discussed. By optimizing the epitaxy process parameters and tightly controlling the production procedure such as cleaning and inspecting, barrel type epitaxial furnace can meet the special requirement for buried layer epitaxial process. The characteristics of the epilayers prepared by barrel type epitaxial furnace were close or equivalent to that by single wafer furnace. The ways to suppress the auto doping in the double buried layer epitaxial process were introduced. The ideal transition width of the epilayers was obtained by the two-step epitaxy.

Epitaxy of GaAs thin film with low defect density and smooth surface on Si substrate

Device-quality GaAs thin films have been grown on miscut Ge-on-Si substrates by metal-organic chemical vapor deposition. A method of two-step epitaxy of GaAs is performed to achieve a high-quality top-layer. The initial thin buffer layer at 360 °C is critical for the suppression of anti-phase boundaries and threading dislocations. The etch pit density of GaAs epilayers by KOH etching could reach 2.25 × 105 cm−2 and high-quality GaAs top epilayers are observed by transmission electron microscopy. The band-to-band photoluminescence property of GaAs epilayers on different substrates is also investigated and negative band shifts of several to tens of meVs are found because of tensile strains in the GaAs epilayers. To achieve a smooth surface, a polishing process is performed, followed by a second epitaxy of GaAs. The root-mean-square roughness of the GaAs surface could be less than 1 nm, which is comparable with that of homo-epitaxial GaAs. These low-defect and smooth GaAs epilayers on Si are desirable for GaAs-based devices on silicon substrates.

Gallium nitride epitaxy on (0001) sapphire

Abstract Two-step epitaxy consisting of low-temperature GaN nucleation layers (NLs) and high temperature (HT) GaN overgrowths, deposited on sapphire (0001) by metal-organic chemical vapour deposition, has been examined by transmission electron microscopy and atomic force microscopy. Results indicate that NLs consist of faceted crystalline islands that exhibit a spread in rotation about the (0001) axis. These islands undergo a metamorphosis on annealing and become rounded. The lateral growth during HT deposition of GaN occurs by the attachment of atomic species to steps associated with the rounded islands, resulting in faceted flat-topped islands. Furthermore, growth occurs preferentially in certain regions which evolve into ‘growth patches’. These patches then grow vertically and laterally over the underlying subgrains. The coalescence of these patches produces a continuous GaN layer. The origins of threading dislocations (TDs) in GaN layers have also been investigated. Results show that the majority of T...

Gallium nitride epitaxy on (0001) sapphire

Abstract Two-step epitaxy consisting of low-temperature GaN nucleation layers (NLs) and high temperature (HT) GaN overgrowths, deposited on sapphire (0001) by metal-organic chemical vapour deposition, has been examined by transmission electron microscopy and atomic force microscopy. Results indicate that NLs consist of faceted crystalline islands that exhibit a spread in rotation about the (0001) axis. These islands undergo a metamorphosis on annealing and become rounded. The lateral growth during HT deposition of GaN occurs by the attachment of atomic species to steps associated with the rounded islands, resulting in faceted flat-topped islands. Furthermore, growth occurs preferentially in certain regions which evolve into ‘growth patches’. These patches then grow vertically and laterally over the underlying subgrains. The coalescence of these patches produces a continuous GaN layer. The origins of threading dislocations (TDs) in GaN layers have also been investigated. Results show that the majority of TDs do not form during the coalescence of islands as was assumed previously. Instead, two possible sources of TDs have been identified: firstly, growth faults in NLs and, secondly, point defects. Partial dislocations associated with the faults in the NLs constitute the major source of basal plane dislocations, which may develop into TDs by self-glide and climb. It has also been suggested that the mosaic structure observed in fully grown GaN layers is due to elastic interactions between TDs, which glide and climb to form subgrain boundaries.

Highly carbon-doped Ga 0.47In 0.53As contact layers grown by using carbontetrabromide in MBE on MOVPE 1.55 μm GaInAsP/InP MQW laser structures

We report on carbon incorporation in (Ga,Al)InAs/InP using carbontetrabromide as the dopant precursor in molecular beam epitaxy. For Ga 0.47In 0.53As we find an increasing free hole concentration with decreasing growth temperature in the range from 450 to 515°C. In contrast, the carbon incorporation is independent of the growth temperature. At 450°C the electrical activation of carbon is almost 100% and free hole concentrations up to 2–3×10 20 cm −3 are achieved. The ratio of free hole concentration to carbon incorporation starts to diminish below 1.0 above hole concentrations of 8×10 19 cm −3. We consider a net selective etching of indium at the growing surface due to the CBr 4 precursor at very high doping levels. For (Ga,Al)InAs growth temperature dependence of the free hole concentration is not observed. Although the supply of CBr 4 is fixed the free carrier concentration and simultaneously the carbon incorporation increase with an increasing aluminium content in the layer. This holds even true for an aluminium mole fraction down to only 0.5%. These results are exploited for producing highly p-doped Ga 0.47In 0.53As contact layers, which are uniform over large areas, on MOVPE grown 1.55 μm GaInAsP/InP MQW laser structures in a two-step epitaxy process. First results on broad area laser structures already show comparable data to MQW laser structures of the same design but completely produced by MOVPE.

In situ surface passivation of III–V semiconductors in MOVPE by amorphous As and P layers

Abstract A new process for chemical passivation of III–V semiconductor surfaces in metalorganic vapour phase epitaxy (MOVPE) is developed. A passivation layer is deposited directly after growth in the reactor. It consists of amorphous arsenic or a double-layer package of amorphous phosphorus and arsenic, which are grown by photo-decomposition of the group-V hydrides. These layers (caps) serve to protect the surfaces against contamination in air after removing the samples from the MOVPE growth reactor. Such passivation is applicable e.g. for a two-step epitaxy or for further surface characterizations.

Two-step MOVPE growth for planar InP/InGaAs/InP pin-FET combinations with locally diffused buffer layer

Abstract Low pressure MOVPE has been developed to prepare planar InP/InGaAs pin-FET photoreceivers in a two-step epitaxy. For the first time, a growth process is described which uses a regrowth over selectively diffused areas to optimize both the pin diode and the FET, without losing planarity. Problems arising from interfacial doping and the regrowth over stressed areas have been investigated. After a short description of the device technology the properties of the pin diode and the FET are discussed.

V-grooved substrate buried heterostructure InGaAsP/InP laser emitting at 1.3 µm wavelength

Details of the fabrication, optimization of the dimensions of the active region, characteristics, and the aging results of the V - grooved substrate buried heterostructure (VSB) InGaAsP/InP laser are described. It is shown that the VSB laser can be fabricated in one-step epitaxy as well as two-step epitaxy. The active region width below 2.5 μm and the thickness of 0.15-0.2 \mu m are shown to give stable fundamental mode operation and good temperature characteristics. The fundamental mode operation up to the optical output of 20 mW/facet at 25°C and the CW operation above 100°C are obtained. The pulse response showed the strongly damped relaxation oscillation with a frequency as high as 4.5 GHz. The spectral width under the modulation of 400 Mbit/s RZ single is as narrow as 25 A in full width at half maximum. Highly stable aging characteristics at an elevated temperature of 50°C are obtained in both two-step epitaxy lasers and one-step epitaxy lasers.

V-Grooved Substrate Buried Heterostructure InGaAsP/lnP Laser Emitting at 1.3 µm Wavelength

Details of the fabrication, optimization of the dimensions of the active region, characteristics, and the aging results of the V-grooved substrate buried heterostructure (VSB) InGaAsP/InP laser are described. It is shown that the VSB laser can be fabricated in one-step epitaxy as well as two-step epitaxy. The active region width below 2.5 µm and the thickness of 0.15-0.2 µm are shown to give stable fundamental mode operation and good temperature characteristics. The fundamental mode operation up to the optical output of 20 mW/facet at 25°C and the CW operation above 100°C are obtained. The pulse response showed the strongly damped relaxation oscillation with a frequency as high as 4.5 GHz. The spectral width under the modulation of 400 Mbit/s RZ single is as narrow as 25 A in full width at half maximum. Highly stable aging characteristics at an elevated temperature of 50°C are obtained in both two-step epitaxy lasers and one-step epitaxy lasers.