Minority Carrier Lifetime In GaAs Research Articles

Monolithic integration of room-temperature cw GaAs/AlGaAs lasers on Si substrates via relaxed graded GeSi buffer layers

GaAs/Al x Ga (1−x) As quantum well lasers have been demonstrated via organometallic chemical vapor deposition on relaxed graded Ge/GexSi(1−x) virtual substrates on Si. A number of GaAs/Ge/Si integration issues including Ge autodoping behavior in GaAs, reduced critical thickness due to thermal expansion mismatch, and complications with mirror facet cleaving have been overcome. Despite unoptimized laser structures with high series resistance and large threshold current densities, surface threading dislocation densities for GaAs/AlGaAs lasers on Si substrates as low as 2×106 cm−2 permitted continuous room-temperature lasing at a wavelength of 858 nm. The laser structures are uncoated edge-emitting broad-area devices with differential quantum efficiencies of 0.24 and threshold current densities of 577 A/cm2. Identical devices grown on commercial GaAs substrates showed similar behavior. This comparative data agrees with previous measurements of near-bulk minority carrier lifetimes in GaAs grown on Ge/GeSi/Si substrates.

Strategies For Direct Monolithic Integration of AlxGa(1−x)As/InxGa(1−x)As LEDS and Lasers On Ge/GeSi/Si Substrates Via Relaxed Graded GexSi(1−x) Buffer Layers

AbstractAlxGa(1−x)As/GaAs quantum well lasers have been demonstrated via organometallic chemical vapor deposition (OMCVD) on relaxed graded GexSi(1−x) virtual substrates on Si. Despite unoptimized laser structures with high series resistance and large threshold current densities, surface threading dislocation densities as low as 2×106 cm−2 enabled cw room-temperature lasing at a wavelength of 858nm. The laser structures are oxide-stripe gain-guided devices with differential quantum efficiencies of 0.16 and threshold current densities of 1550A/cm2. Identical devices grown on commercial GaAs substrates showed differential quantum efficiencies of 0.14 and threshold current densities of 1700A/cm2. This comparative data agrees with our previous measurements of near-bulk minority carrier lifetimes in GaAs grown on Ge/GeSi/Si substrates. A number of GaAs/Ge/Si integration issues including thermal expansion mismatch and Ge autodoping behavior in GaAs were overcome.

High minority-carrier lifetimes in GaAs grown on low-defect-density Ge/GeSi/Si substrates

A high bulk minority-carrier lifetime in GaAs grown on Si-based substrates is demonstrated. This was achieved by utilizing a step-graded Ge/GeSi buffer (threading dislocation density 2×106 cm−2) grown on an offcut (001) Si wafer, coupled with monolayer-scale control of the GaAs nucleation to suppress antiphase domains. Bulk minority-carrier lifetimes (τp) were measured using room-temperature time-resolved photoluminescence applied to a series of Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As double-heterojunction structures doped n=1.1×1017 cm−3 with GaAs thicknesses of 0.5, 1.0, and 1.5 μm. A lifetime τp=7.7 ns was determined for GaAs grown on Si. The extracted interface recombination velocity of 3.9×103 cm/s is comparable to recombination velocities found for Al0.3Ga0.7As/GaAs interfaces grown on both GaAs and Ge wafers, indicating that the crosshatch surface morphology characteristic of strain-relaxed Ge/GeSi surfaces does not impede the formation of high-electronic-quality interfaces. These results hold great promise for future integration of III–V minority-carrier devices with Si wafer technologies.

Aspects of “High Minority-Carrier Lifetime” GaAs on Si Using A Novel SiGe/Ge Buffer

Heteroepitaxial GaAs-on-Si utilizing a Si 0.4 Ge 0.96 /Ge buffer, with a hole minority-carrier lifetime as long as ∼ 2.5 nsec is described. This is the longest minority-carrier lifetime in GaAs grown on Si reported to date by any approach. Here we discuss the microstructural aspects of this heteroepitaxial system, including a crossectional transmission electron microscopy (XTEM) study of the interface of the SiGe/Ge buffer and the role of the SiGe layer. An x-ray double crystal diffraction (DCD) study of the GaAs layers is also presented. The SiGe/Ge buffer approach to heteroepitaxial GaAs on Si is a result of two observations: (1) SiGe epitaxial layers grown on Ge are under biaxial compressive stress (from DCD) and (2) dislocations tend to bend over into the Ge substrate (from TEM). These data and a description of the heteroepitaxy of SiGe layers on Ge are presented.

Ultralong minority-carrier lifetimes in GaAs grown by low-pressure organometallic vapor phase epitaxy

We have measured minority-carrier lifetimes of up to 4.9 μs in GaAs layers that have been grown by low-pressure organometallic vapor phase epitaxy. These lifetimes, representing a major improvement compared with previously obtained results, are governed by radiative recombination processes. Carbon incorporation during crystal growth at low arsine partial pressures is of prime importance in understanding the origin of these very long lifetimes.

High-pressure dependence of the room-temperature minority carrier lifetimes in GaAs

Photoluminescence decay measurements on n-GaAs under pressure indicate the appearance of a hole recombination centre at p approximately=2 GPa. This can be ascribed to DX centres with a hole capture cross section of 10-16 cm2.

Measurement of minority carrier lifetime in GaAs and GaAs 1−xP x with an intensity-modulated electron beam

A new method of measuring short minority carrier lifetimes with a Scanning Electron Microscope (SEM) is reported. Main features are high spatial resolution (3 ωm in GaAs at 30 keV energy of beam electrons) and the insensitivity to surface recombination by use of a Schottky-contact. The shortest measurable lifetime is approx. 100 ps depending on sample conditions. The minority carrier lifetime is evaluated from the phase rotation between the measured ac-EBIC and the ac-component of the intensity modulated electron beam. The diffusion length required for the analysis is measured by the collection efficiency of the Schottky-contact, similar to the method of Wu and Wittry. Application of the method is demonstrated with a GaAs sample and a GaAs 1− x P x sample. EBIC micrographs (phase and amplitude) show local flucuations of lifetime and diffusion length.

Measurement of minority-carrier lifetime in GaAs using the transient response of MOS capacitors

The minority-carrier generation lifetime has been measured in GaAs by observing the transient capacitance that occurs when an MOS is switched from accumulation to deep depletion. Application of this technique requires the fabrication of an MOS that shows inversion; this has been done by growing a native GaAs oxide with plasma oxidation. Preliminary results are reported on both lifetime and surface recombination velocity in p-type GaAs.