Michael Joseph Cich

Bulk GaN based violet light-emitting diodes with high efficiency at very high current density

We present experimental results on III–nitride light-emitting diodes emitting at 410 nm, grown on low-defectivity bulk GaN substrates. The epitaxial layers are optimized for high peak efficiency and maintain efficiency at very high current densities. We use a volumetric device architecture with surface roughness to maximize light extraction efficiency. We report an external quantum efficiency of 68% at 180 A cm−2. No current crowding is observed at high current density. We also demonstrate flat-line reliable operation to over 1000 h.

Bulk GaN flip-chip violet light-emitting diodes with optimized efficiency for high-power operation

We report on violet-emitting III-nitride light-emitting diodes (LEDs) grown on bulk GaN substrates employing a flip-chip architecture. Device performance is optimized for operation at high current density and high temperature, by specific design consideration for the epitaxial layers, extraction efficiency, and electrical injection. The power conversion efficiency reaches a peak value of 84% at 85 °C and remains high at high current density, owing to low current-induced droop and low series resistance.

High light extraction efficiency in bulk-GaN based volumetric violet light-emitting diodes

We report on the light extraction efficiency of III-Nitride violet light-emitting diodes with a volumetric flip-chip architecture. We introduce an accurate optical model to account for light extraction. We fabricate a series of devices with varying optical configurations and fit their measured performance with our model. We show the importance of second-order optical effects like photon recycling and residual surface roughness to account for data. We conclude that our devices reach an extraction efficiency of 89%.

Analysis of twin defects in GaAs(111)B molecular beam epitaxy growth

The formation of twin is common during GaAs(111) and GaN(0001) molecular beam epitaxy (MBE) metalorganic chemical vapor deposition growth. A stacking fault in the zinc-blende (ZB)(111) direction can be described as an insertion of one monolayer of wurtzite structure, sandwiched between two ZB structures that have been rotated 60° along the growth direction. GaAs(111)A/B MBE growth within typical growth temperature regimes is complicated by the formation of pyramidal structures and 60° rotated twins, which are caused by faceting and stacking fault formation. Although previous studies have revealed much about the structure of these twins, a well-established simple nondestructive characterization method which allows the measurement of total aerial density of the twins does not exist at present. In this article, the twin density of AlGaAs layers grown on 1° miscut GaAs(111)B substrates has been measured using high resolution x-ray diffraction, and characterized with a combination of Nomarski microscopy, atomi...

Generation-recombination low-frequency noise signatures in GaAs metal–semiconductor field-effect transistors on laterally oxidized AlAs

Low-frequency noise characteristics of GaAs-on-insulator metal–semiconductor field-effect transistors, for which the insulating buffer layer was produced by lateral wet-oxidation of AlAs, are studied. Devices with different gate widths were fabricated resulting in different overoxidation times for the AlAs layer. Three characteristic generation-recombination noise signatures are observed depending on the measurement temperature and the gate bias. A generation-recombination noise signature with energy level at Ec−0.69 eV is found to increase with the amount of overoxidation time. This near midgap trap shows an increase in concentration towards the oxide interface, and it is tentatively assigned to an arsenic-antisite-related defect known from previous studies as EB4. A possible mechanism for the formation and the microscopic origin of this defect are discussed.

Influence of gas transport on the oxidation rate of aluminum arsenide

The effect of gas transport on the lateral oxidation kinetics of aluminum arsenide has been studied by limiting the gas transport to the gas–oxide interface using closely spaced mesas. At 440 °C the gas transport factor is found to be 8.5±1.3 times the reaction rate coefficient, resulting in a measurable decrease in oxidation rate for mesas closer than 200 nm. This confirms the usual assumption that the initial oxidation rate is limited by the reaction kinetics at the oxidizing interface and not the gas transport for normal oxidation conditions

In situ diffuse reflectance spectroscopy investigation of low-temperature-grown GaAs

We have utilized in situ diffuse reflectance spectroscopy (DRS) to monitor both the substrate temperature transient and the epilayer absorption during low-temperature (LT) GaAs molecular-beam epitaxy. We have found a significant increase of the sub-band-gap absorption from LT GaAs. The magnitude of absorption at 1.2 eV correlates well with the concentration of arsenic antisite defects. The incorporation rate of arsenic antisites appears uniform despite a substrate temperature transient due to the effusion cell radiation heating. The influence of absorption spectra change on the accuracy of DRS temperature measurement is also discussed. This study shows that DRS can be used for both growth temperature measurement and real-time nonstoichiometry monitoring.

AFM study of lattice matched and strained InGaAsN layers on GaAs

We studied strained & lattice matched InGaAsN, InGaAs, and GaAsN layers, grown on GaAs substrate with gas source molecular beam epitaxy. Nitrogen concentration and lattice-matched condition have been established from Vegards law with X-ray diffraction. Atomic force microscope measurement, at 22-monolayer thickness, shows different growth mechanism for each composition. Especially, a mesh-like surface morphology of lattice matched InGaAsN has been revealed in this study.

Final report on LDRD project 105967 : exploring the increase in GaAs photodiode responsivity with increased neutron fluence.

A previous LDRD studying radiation hardened optoelectronic components for space-based applications led to the result that increased neutron irradiation from a fast-burst reactor caused increased responsivity in GaAs photodiodes up to a total fluence of 4.4 x 10{sup 13} neutrons/cm{sup 2} (1 MeV Eq., Si). The silicon photodiodes experienced significant degradation. Scientific literature shows that neutrons can both cause defects as well as potentially remove defects in an annealing-like process in GaAs. Though there has been some modeling that suggests how fabrication and radiation-induced defects can migrate to surfaces and interfaces in GaAs and lead to an ordering effect, it is important to consider how these processes affect the performance of devices, such as the basic GaAs p-i-n photodiode. In this LDRD, we manufactured GaAs photodiodes at the MESA facility, irradiated them with electrons and neutrons at the White Sands Missile Range Linac and Fast Burst Reactor, and performed measurements to show the effect of irradiation on dark current, responsivity and high-speed bandwidth.

Position and mode dependent coupling of terahertz quantum cascade laser fields to an integrated diode

A Schottky diode integrated into a terahertz quantum cascade laser waveguide couples directly to the internal laser fields. In a multimode laser, the diode response is correlated with both the instantaneous power and the coupling strength to the diode of each lasing mode. Measurements of the rectified response of diodes integrated in two quantum cascade laser cavities at different locations indicate that the relative diode position strongly influences the laser-diode coupling. ∗ Now at Soraa, Freemont, California, 94555 USA † mcwanke@sandia.gov 1 ar X iv :1 60 5. 03 11 8v 1 [ co nd -m at .m es -h al l] 1 0 M ay 2 01 6 Quantum cascade lasers (QCLs) may be considered one of the most remarkable achievements in quantum engineering due to both the intensity and the broad tailorability of their emission. Since the operating range of these unipolar, intersubband lasers was extended to the terahertz (THz) band of the spectrum, a variety of applications requiring a compact high-power (>mW) source between 1-5 THz have become accessible. Of particular interest is the use of a THz QCL as a local oscillator (LO) for heterodyne mixing. THz QCLs provide ample power for mixing; however, it is non-trivial to efficiently couple the THz LO power from a QCL to a mixer such as a planar Schottky diode. One possible solution is to directly integrate a Schottky diode mixer into the core of a THz QCL to create a THz transceiver. We previously observed the direct coupling of the internal QCL fields to an integrated diode, however, several questions concerning the precise nature of this coupling remain open. For practical applications, the response of a Schottky diode mixer should be linear in both the LO and signal field amplitudes. However, prior measurements suggested that both the mode structure and the instantaneous power of the laser may affect the laserdiode coupling and lead to a non-linear response to the QCL (LO) power. In this letter we examine how the rectified response of Schottky diodes embedded into the core of THz QCLs depends upon diode position and QCL bias current. To determine the effect of diode position upon the diode’s coupling with the laser fields, we compare the rectified response of diodes with different relative positions in the laser waveguide to the emission spectra of two otherwise identical 2.8 THz QCL transceivers. The studied THz QCLs have a Schottky diode embedded into the core of the 3 mm long by 170 μm wide waveguide, as illustrated in Fig. 1. Both transceivers were cleaved from the same row of the processed die, and thus have identical cavity lengths. Sample A has the diode located by design at the center of the QCL waveguide relative to the laser facets, 1.5 mm from both facets. Sample B has the diode shifted +4 μm from that of the diode in Sample A. Given the slight uncertainty of the cleave planes relative to the diode position, the exact locations of the diodes in Samples A and B may differ from design. But the relative positions of the two diodes are fixed by the device layouts. Rectified and intermediate frequency (IF) signals result from the coupling of THz laser fields to a Schottky diode. If only nearest-neighbor modes in a Fabry-Perot laser (FP) cavity separated by the angular frequency ωFP are considered, the rectified and IF signals,