Vertical-Cavity Surface-Emitting Lasers are making up a large and growing share of the world’s production of semiconductor lasers. But the 850 nm GaAs quantum well VCSELs that make up most of present product are highly vulnerable to dislocation networks. In this paper, we discuss how materials selection affects the reliability of semiconductor lasers generally. We then describe the most common failure mechanisms observed in VCSELs, and what precautions are used to prevent them. We finish with a brief discussion of reliability testing and failure analysis.

Catastrophic degradation of high power laser diodes is due to the generation of extended defects during the laser operation. The stress necessary for is induced by temperature gradients generated by local enhancement of the temperature due to non radiative recombination and subsequent laser self absorption. The thermal stresses induced by such temperature gradient are calculated using finite element methods, showing that the yield strength can be surpassed. The thermal conductivity of the laser structure is shown to play a relevant role in the process.

Deep-level densities of p-GaAs1−xBix and at the GaAs/p-GaAs1−xBix heterointerface have been shown to be sufficiently low for device applications based on the results of deep-level transient spectroscopy, isothermal capacitance transient spectroscopy and admittance spectroscopy. Although the metastable alloy of GaAs1−xBix is grown by molecular beam epitaxy at low temperature (370 °C), the deep-level density of p-GaAs1−xBix is suppressed such that it is on the order of 1015 cm−3. The state density at the heterointerface was determined to be 8 · 1011 cm−2eV−1, which is comparable to other III–V heterointerfaces formed at high temperatures. The surfactant-like effect of Bi is believed to prevent defect formation during low-temperature growth.

Within the framework of a grand partition function formalism, we examine the occupancy of the dangling bond dislocation defect sites and the VGa-ON dislocation defect sites within uncompensated n-type gallium nitride. The sensitivity of these results to variations in the unoccupied dislocation defect energy level is examined. We find that the VGa-ON dislocation defect sites’ greater capacity to store charge plays a large role in influencing the results, i.e., greater free electron and bulk donor concentrations are required in order to fully saturate the threading dislocation lines with charge.

MgZnO becomes amorphous or short-range-ordered with the addition of hafnium oxide. The films are rf-sputter deposited onto glass substrates (Eagle 2000, Corning Inc.) from Mg0.05HfxZn0.95-xO targets (x=0, 0.025, 0.05, 0.075, 0.1) in pure Ar ambient at room temperature. The sputtered Mg0.05Zn0.95O exhibits strong (002) preferred orientation with XRD peak located at 2θ=34.16o. The XRD peak intensity is also greatly reduced, indicating the material amorphorization proceeds with the addition of Hf. The grain size, estimated from the full-width-at-half-maximum (FWHM) of the (002) XRD peak, decreases from 24.1 to 3.3 nm as the Hf content x increases from 0 to 0.025 in Mg0.05HfxZn0.95-xO. No sharp XRD peaks are detected in the as-sputtered films when more than 5.0 at.% Hf are added into the materials. The films remain in amorphous or short-range-ordered states after annealing at 600 oC for 30 mins. All Mg0.05HfxZn0.95-xO films (100 nm in thickness) are highly transparent (> 80 %) in the visible region from 400 to 800 nm and have sharp absorption edges in the UV region. The tauc bandgap ΔE (eV), as a function of hafnium composition x, is fitted as ΔE=3.336+6.08x for room temperature as-deposited films, and ΔE=3.302+2.60x for films after 30 min 600 oC annealing. The annealing process decreases the bandgap shift caused by the incorporation of Hf in the materials.

Initial tests are performed regarding the degradation of lattice-mismatched GaInAs solar cells. 1eV metamorphic GaInAs solar cells with 1-2×106 cm-2 threading dislocation density in the active region are irradiated with an 808 nm laser for 2 weeks time under a variety of temperature and illumination conditions. All devices show a small degradation in Voc that is logarithmic with time. The absolute loss in performance after 2 weeks illuminated at 1300 suns equivalent and 125°C is 7 mV Voc and 0.2% efficiency, showing these devices to be relatively stable. The dark current increases with time and is analyzed with a two-diode model. A GaAs control cell degrades at the same rate, suggesting that the observed degradation mechanism is not related to the additional dislocations in the GaInAs devices.

We studied the polarization-dependent photoluminescence (PL) of a-plane GaN /AlGaN multiple quantum wells (MQWs) grown on r-plane sapphire substrate with the various well width from 1.5 to 7.33 nm. To clarify the reasons of light emission polarization properties, we applied the 6×6 k‧p model to simulate the E-k dispersion relation and the wave functions to obtain the polarization optical transitions. According to the experimental result, the PL emission peak position exhibits a red-shifted with increasing well width, due to the reduction of the quantum confinement effect. The polarization ratio of a-plane GaN/AlGaN MQWs increased from 0.236 to 0.274 with increasing the quantum well width. This phenomenon is believed to be that y-polarized light emission gradually dominates the PL spectrum and thus enhances the polarization ratio.

By pumping AlGaN/GaN HEMTs with below band-gap light we observe changes in drain current that correspond to the trapping and detrapping of carriers within the band-gap. These changes in drain current are indicators of trap density, since the energy from a specific wavelength of light pumps traps whose activation energies are less than or equal to that of the light source.

AlGaN/GaN HEMTs on SiC with dual submicron gates with widths of 125nm, 140nm, or 170nm, are DC-stressed under three different conditions along a load line: VGS=0, VDS=5 (on-state), VGS=-2, VDS=9.2 and, VGS=-6, VDS=25 (off-state). The stress tests are interrupted at 20% degradation and the optically pumped comparisons to the baseline are measured.

This paper describes the optical pumping technique and results from experiments of AlGaN/GaN HEMTs under the three DC stress biases along a load line.

We present results on optical degradation of gallium nitride based materials under low energy electron beam irradiation (LEEBI). GaN thin film and GaN/InGaN quantum well samples, grown by metal-organic vapor phase epitaxy (MOVPE), were exposed to a tightly focused (ø = 2 nm, J = 0-130 kA/cm2), rapidly scanning electron beam (e-beam) with energy of 5-20 keV and dose of 0-500 μC/cm2. The irradiation severely reduced the band-to-band photoluminescence of the exposed sample areas. Performing positron annihilation spectroscopy measurements on the irradiated films revealed an important increase of Ga-vacancy concentration as a function of the irradiation dose. Based on the measurements we propose that in-grown passive VGa-Hn complexes are present in MOVPE grown GaN (and its alloys), and are activated by LEEBI.

High reliability, low power consumption and high speed laser diodes are required for optical interconnect. We developed 1060nm VCSELs with InGaAs/GaAs strained quantum wells, oxide-confined and double intra-cavity structures for that purpose. As for the power consumption, low power dissipation of 0.14 mW/Gbps at 10 Gbps operation has been achieved. Clear eye openings up to 20 Gbps were confirmed at a low bias current of 5 mA. In the reliability test, accelerated aging tests were performed up to 5,000 hours at 6 mA in three different temperatures, 70 oC, 90 oC and 120 oC. The total number of the VCSELs was 4,898 pcs (approximately 5,000). No failure was observed. Under the normal operating condition of 40 oC and 6 mA, the total device-hours was 7.75×107 hours assuming Ea = 0.35 eV according to Telcordia GR-468-CORE. The random failure rate of 30 FIT with the confidence level (C.L.) of 90 % and 12 FIT with the C.L. of 60 % were estimated. To estimate the wear-out lifetime and the number of FITs, high stressed aging tests with 170 oC and 6 mA were performed. With the acceleration factor of Ea = 0.7 eV in the wear-out failure, the median lifetime was 3,000 hours which was equivalent to 300 years in 40 oC ambient. The FIT numbers due to the wear-out were estimated as 0.3 FIT for 10 years. Compared with the random failure rate of 30 FIT, the wear-out failure rates are considered to be negligible. In the extremely long term aging test with 90 oC and 6 mA, no wear-out trend has been observed in both threshold current and optical power up to 20,000 hours operation. These results indicate that 1060 nm VCSEL is promising light source used in optical interconnect for high performance computers and data centers.

The insertion of nanostructured materials (such as quantum wells, wires, and dots) into the intrinsic region of p-i-n solar cells introduces an intermediate band within the bandgap of the host material. It has been shown that the sub-bandgap conversion provided by the nanostructured materials, enhances the short circuit current as well as the overall efficiency of InAs quantum dots (QD) imbedded in GaAs superlattice (SL) solar cells [1]. As a contender for space applications, it is necessary to subject these solar cell structures to temperatures encountered in the Low Earth Orbit (LEO), probing for any material degradation. Herein, we focus on temperature dependent characterization using high resolution X-ray diffraction (HRXRD) of InAs QD enhanced GaAs solar cell structures with varying growth parameters. The structures characterized can be classified into three groups: (1) GaP strain compensation coverage, (2) GaAs barrier coverage, and (3) InAs coverage for QD formation. HRXRD rocking curves of each structure focusing around the GaAs peak are analyzed at a range of temperatures up to 200˚C. Although no noticeable shifts in the SL peaks are detected, interfacial diffusion decreased the resolution of fringes produced by reflections at the SL interfaces in test structures with varying InAs QD coverage. Unbalanced strain in the same structures shows a distortion in the GaAs peaks.

Nitrogen-doped ZnO (ZnO:N) films have been prepared by remote plasma atomic layer deposition (RP-ALD) and treated by rapid thermal annealing (RTA) in oxygen atmosphere. The local electronic structures of the (ZnO:N) films were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES) at the O K-edge. The XPS reveals the presence of the Zn-N bond in the ZnO:N films, indicating that partial amounts of oxygen sites are occupied by nitrogen species. This is correspondent with the decrease of electron concentration in ZnO:N films with the nitrogen doping concentration, as indicated by the Hall effect measurement. The RP-ALD technique was applied to fabricate the n-type ZnO:N/p-type GaN heterojunction LEDs. Dominant ultraviolet electroluminescence at 371 nm from the ZnO:N layer was observed at room temperature.

Charge trapping and slow (10 s to > 1000 s) detrapping in AlGaN/GaN HEMTs designed for high breakdown voltage (> 1500 V) are studied to identify the impact of Al molefraction and passivation on trapping. Two different trapping components, TG1 (Ea = 0.62 eV) and TG2 (with negligible temperature dependence) in AlGaN dominate under gate bias stress in the off-state. Al0.15Ga0.85N shows much more vulnerability to trapping under gate stress in the absence of passivation than does AlGaN with a higher Al mole fraction. Under large drain bias, trapping is dominated by a much deeper trap TD. Detrapping under illumination by monochromatic light shows TD to have Ea ≈ 1.65 eV in Al0.26Ga0.74N and Ea ≈ 1.85 eV in Al0.15Ga0.85N. This is consistent with a transition from a deep state (Ec - 2.0 eV) in the AlGaN barrier to the 2DEG.

Boron Phosphide (BP) is a promising material for use as a room temperature semiconductor detector of thermal neutrons. The absorption of a thermal neutron by a 10B nucleus in BP can yield 2.3MeV of energy which in solid state BP can yield ∼0.5 million electron-hole pairs that would be detectable with minimal amplification in a device. BP thin films are grown according to the net reaction below in a cold wall chemical vapor deposition (CVD) reactor: Thin film depositions are performed using diborane and phosphine with a balance of hydrogen gas at near atmospheric pressure with RF induction heating. The resultant BP films are characterized by Raman, XRD, SEM, TEM and TEM-EELS for chemical composition, surface and bulk morphology. BP growths on Si and SiC substrates are compared. SiC provides reduced lattice mismatch for growth of BP and growth of heteroepitaxial BP on SiC will be discussed.

Gallium nitride thin films were grown by pulsed laser deposition. Subsequently, post-growth annealing of the samples was performed at 400, and 600 oC in the nitrogen atmosphere. Surface morphology of the as-grown and annealed samples was performed by atomic force microscopy, surface roughness of the films improved after annealing. Chemical analysis of the samples was performed using x-ray photon spectroscopy, stoichiometric Gallium nitride thin films were obtained for the samples annealed at 600 oC. Optical measurements of the samples were performed to investigate the effect of annealing on the band gap and optical constants the films.

Possibility of feedback and inflation mechanism among carrier captures by a deep-level defect and transient induced lattice vibrations is discussed using proper configuration coordinate diagrams for many carriers. Treating the lattice motion classically we selfconsistently simulate the time evolution of the interaction mode and a series of athermal captures of electron(s) and hole(s). When both the activation energies Eacte and Eacth are small, a series of successive athermal captures is enhanced and probable for high carrier densities, however, we find that the possibility of inflation in the amplitude of the lattice vibration critically depends on the minority capture rate and the relative width of the phonon frequency distribution.

In this work, we present a method able to fabricate thin GaN nanomembranes fit for device applications. Starting from commercial GaN on sapphire substrates, MBE was used to deposit a sacrificial layer, which comprises of a superlattice of InN/InGaN, after which thin a GaN film of hundreds of nanometers thickness was grown on top. Pulsed laser irridiation with photon energy of 2.3eV gives rise to the controlled decomposition of the sacrificial intermediate layer, which can be followed by easy separation of the top GaN membrane from the substrate. This process can be used to manufacture GaN membranes with low defect density and a wider range of thickness. We demonstrated that large area, free-standing GaN membranes, with a thickness from 200nm and up, could be made using this method, and the high crystal quality of the lift-off GaN layers is well preserved in this process.

In this paper, we describe highly reliable GaN high electron mobility transistors (HEMTs) for high-power and high-efficiency amplifiers. First, we present the reliability mechanisms and progress on the previously reported GaN HEMTs. Next, we introduce our specific device structure of GaN HEMTs for improving reliability. An n-GaN cap and optimized buffer layer were used to suppress the trap-related phenomena, such as a current collapse. Gate edge oxidation is effective for reducing the gate leakage current. A Ta-based barrier metal was inserted between an ohmic electrode and interconnection metal for preventing increase in contact resistance. SiN of passivation film was optimized for reducing the current collapse of short-gatelength HEMTs.