A. K. Chin

Defect mechanisms in degradation of 1.3-μm wavelength channeled-substrate buried heterostructure lasers

Channeled-substrate buried heterostructure (CSBH) lasers which were purged from populations undergoing high reliability qualification have been studied in detail. Gradual and rapid degradation mechanisms leading to accelerated aging failure modes have been analyzed by transmission electron microscopy, convergent beam electron diffraction, electroluminescence, energy dispersive x-ray analysis, and chemical etching. The gradual degradation mode of CSBH lasers is characterized by (1) a gradual increase in room-temperature threshold current; (2) a decrease in external quantum efficiency, typically a drop in peak value of dL/dI greater than 25%; (3) a drop in forward voltage at low current, indicating a change in junction characteristics; (4) a large peak inI(dV/dI) below threshold (at around 3 mA); and (5) an enhancement in the peak in I2(d2V/dI2) at laser threshold. A defect mechanism associated with the gradual degradation begins with a nucleation of extrinsic dislocation loops along the V-groove {111} p-n–...

Effects of thermal annealing on semi‐insulating undoped GaAs grown by the liquid‐encapsulated Czochralski technique

Recently, a number of studies have reported a correlation between variations in threshold voltage of field effect transistors and the nonuniformity of the luminescence efficiency of semi‐insulating GaAs crystals grown by the liquid‐encapsulated Czochralski technique. The changes in luminescence efficiency and subsequently the variations in threshold voltages were dramatically reduced by postgrowth annealing of the GaAs crystals under a variety of conditions. In this study, we employ the technique of spatially resolved cathodoluminescence (CL) to carefully examine the changes in luminescence efficiency due to postgrowth annealing. In agreement with previous work, we find that the CL variations are greatly reduced from a factor of ∼2 to ∼5% by thermal annealing at 800 °C for 30 h or at 1200 °C for 6 h followed by slow cooling. The latter thermal treatment is the same as that experienced by crystals during growth by the horizontal gradient freeze (HGF) technique. The extremely uniform luminescence efficiency...

Direct evidence for the role of gold migration in the formation of dark‐spot defects in 1.3‐μm InP/InGaAsP light‐emitting diodes

The results of our previous study of dark‐spot defects (DSD’s) in aged 1.3‐μm InP/InGaAsP light‐emitting diodes (LED’s) have strongly suggested that the defects form as a result of the migration of gold from the p contact into various epitaxial layers. To provide further support for this degradation mechanism, we compare, in this study, the formation of DSD’s in LED’s fabricated with the usual BeAu p metallization and a new platinum p contact. After accelerated aging (200 °C junction temperature, 20 kA/cm2, 3×103 h), DSD’s were observed only in the devices with BeAu contacts, thus directly identifying the active role of gold migration in DSD formation.

Reliability of InGaAsP light emitting diodes at high current density

InGaAsP LEDs emitting at 1.3 µm are attractive sources for long distance transmission systems. These devices have been shown to have excellent reliability at 8 kA/cm2. In order to launch more power into the optical fiber it is desirable to operate at the highest possible current densities consistent with system reliability requirements. In this work, the high temperature aging behavior of these LEDs has been studied at current densities from 20 to 40 kA/2. Both the standard LED structure, where the small diameter p-contact is isolated with a dielectric layer, and a structure in which a Schottky barrier is used for isolation are examined. Dark spot defect (DSD) formation is greatly enhanced at these high current densities in devices with dielectric isolation, limiting MTTF atT_{J} = 70\degC to 2 \times 10^{5}h. In contrast, devices with Schottky-barrier isolation remain essentially free of DSDs and haveMTTF > 10^{7}h at 70°C. These results suggest that stress from the dielectric layer promotes the growth of DSDs. Schottky-barrier devices in which the dielectric layer is eliminated are, thus, better suited for high current-density operation.

Cathodoluminescence evaluation of dark spot defects in InP/InGaAsP light‐emitting diodes

In this study, the formation of dark spot defects (DSD’s) in InP/InGaAsP light‐emitting diodes (LED’s) is evaluated by cathodoluminescence imaging and energy dispersive x‐ray spectroscopy (EDS). Defects resulting in DSD’s are shown to be located in either the p‐InGaAsP contact layer, the p‐InP confining layer, or the InGaAsP active layer. The presence of gold was not detected at the DSD’s using EDS. However, gold was found in the form of submicron‐sized inclusions in the contact layer and confining layer of cylindrically lapped wafers using EDS. Our results strongly suggest that the migration of gold from the p contact during device processing and aging results in the formation of DSD’s in InP/InGaAsP LED’s.

Uniformity characterization of semi‐insulating GaAs by cathodoluminescence imaging

Miyazawa et al. [Appl. Phys. Lett. 43, 853 (1983)] have recently established a spatial correlation between variations in field‐effect transistor performance and nonuniformities in the cathodoluminescence (CL) efficiency of semi‐insulating (SI) GaAs substrates. In this study, we compare the CL uniformity of both Cr‐doped and undoped SI GaAs crystals grown by the liquid‐encapsulated Czochralski (LEC) technique with undoped SI crystals grown by the horizontal gradient freeze (HGF) technique. In contrast to the LEC crystals, HGF GaAs has extremely uniform CL characteristics which should result in uniform device performance.

The migration of gold from the p-contact as a source of dark spot defects in InP/InGaAsP LED's

In this paper, the formation of dark spot defects (DSDs) in InP/InGaAsP LEDs is studied by cathodoluminescence (CL) imaging, electron-beam-induced-current (EBIC) imaging, Auger electron spectroscopy (AES), and energy dispersive X-ray spectroscopy (EDS). Defects resulting in DSDs are shown by CL and EBIC to be located in either the p-InGaAsP contact layer or the p-InP confining layer for short aging times. For longer aging times, these defects are also found in the InGaAsP active layer. The presence of gold was not detected at the DSDs using EDS. However, gold was found in the form of submicron size inclusions at the contact layer-confining layer interface of cylindrically-lapped wafers using AES and EDS. Our results strongly suggest that the migration of gold from the p-contact during device processing and aging results in the formation of DSDs in InP/InGaAsP LEDs.

Failure mode analysis of planar zinc‐diffused In0.53Ga0.47As p‐i‐n photodiodes

In order to understand the irreversible failure mechanisms of planar InGaAs p‐i‐n photodiodes, 32 devices from 19 different wafers that shorted during aging were first examined in the scanning electron microscope. Included were devices that failed during long term aging (>103 h) as well as those that failed during short term aging (<102 h) at higher reverse bias. With a few exceptions, the diodes failed as a result of a single localized leakage source located at the perimeter of the p‐n junction. Three types of leakage sources were found: (a) a microplasma, (b) a microplasma associated with a region of high recombination rate, and (c) a microplasma associated with a thermally damaged region. Analysis of ∼40 devices before and after aging shows that leakage paths found after aging result from microplasmas initially present in the device. Defect analysis shows that neither threading dislocations nor misfit dislocations are generally responsible for these microplasmas. Analysis of the processing shows that t...

Formation of p+‐p−‐n− junctions in InP by Cd diffusion

A study was made of the diffusion of Cd into nominally undoped (4×1016 cm−3) n‐type InP using elemental sources consisting of (Cd and In) or (Cd and P). Two diffusion fronts whose depths are controlled by the amount of P or In in the diffusion source were delineated by etching. Electron beam induced current profiles and photoluminescence measurements revealed the formation of a  p+‐ p−‐ n− junction, with the  p− region bounded by the two diffusion fronts. Mesa p+‐ p−‐ n− diodes, 150 μm in diameter, fabricated from a wafer with the p+‐ p− and p−‐ n− junctions at 3.1 and 20.0 μm, respectively, have reverse breakdown voltages between 90 and 220 V and reverse leakage currents from 5 to 10 pA at half breakdown. The I‐V characteristics of these p+‐p−‐n− diodes exceed those of state of the art, abrupt p+‐n− InP avalanche photodiodes because of the formation of the p− region.

Light‐current characteristics of InGaAsP light emitting diodes

Light‐current characteristics of 1.3‐μm InGaAsP light emitting diodes were investigated as a function of temperature between 70 and 350 K. The sublinearity of the light output found at high injection levels was shown to be temperature independent and similar in magnitude to that observed in GaAlAs devices. These experimental results cannot be explained with the previously proposed models of in‐plane superluminescence and Auger recombination.