Dicing Induced Damage in GaP Electroluminescent Diodes

Abstract

Batch processing of GaP electrolumineseent (EL) diodes requires that the GaP wafer be separated into individual devices before lead bonding and final packaging. This paper describes an investigation of the effects of this mechanical dicing operatlon on the EL characteristics of GaP diodes. Chemical etching of the diced GaP diode after lead bonding has been found to be essential in achieving the maximum quantum efficiency of the completed device. The etchant used is a 3: I: 1 solution of H2804, 33% H202, and H20 at 60~ The quantum efficiency is found to be dependent on the etching time with the efficiency reaching a maximum after approximately 5 rain.Efficiency and current-voltage measurements on unetched devices indicate the presence of surface leakage currents which decrease the external quantum efficiency of the completed device. Since it is believed that the presence of a damaged surface layer and its associated strain field can provide nonradiative leakage current paths, x-ray topography has been used to detect the existence of dicing-induced strain fields and to follow their removal as a function of etch time. X-ray topographs have also been obtained for samples initially cut with a wire saw and a diamond saw. Etching of the completed GaP diode effectively relieves the dicing-induced strain field and eliminates the surface leakage paths. This results in a device with maximum quantum efficiency and with reproducible current-voltage characteristics.

Gallium Migration Through Contact Metallizations on GaP

“…However, the contacts to GaP cannot be characterized as nonreactive with respect to the oxidation process. Formation of gallium and phosphorus oxides on the gold-based ohmic contacts (2,3) to GaP during galvanic oxidation (1) has been established from electron microprobe analysis (4). It is believed that the presence of oxides on the surfaces of the contacts could be the cause of subsequent bonding difficulties.…”

“…In this work, the origin of the gallium and phosphorus on the surfaces of the contacts to GaP has been investigated by means of secondary ion mass spec-trometry ~ (SIMS). This technique can provide (i) indepth mass spectrometric analyses and (it) ion image displays of sputtered secondary ions generated by a high energy primary ion beam impinging on the specimen (1,(0)(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). With these options, a relative chemical composition profile with depth can be obtained (provided no artifacts are introduced due to relative sputtering yields of the various components of the metallizations) or the area uniformity for a particular species at a given depth can be observed.…”

Reproducible High-Efficiency GaP Green-Emitting Diodes Grown by Overcompensation

“…At this voltage the current is typically dominated by deepstate space charge current (6). The current through the overcompensated and both good and poor standard diodes was typically < 7 • 10 -5 A/cm% Larger currents were not observed in the overcompensated diodes, while occasionally a larger current was measured in a standard diode which correlated with a low EL efficiency (2).…”

“…To check whether the improved reproducibility of the overcompensated diodes is due to a uniform reduction of the space charge current, the current through the diodes at a forward bias of 1.4V was measured. At this voltage the current is typically dominated by deepstate space charge current (6). The current through the overcompensated and both good and poor standard diodes was typically < 7 • 10 -5 A/cm% Larger currents were not observed in the overcompensated diodes, while occasionally a larger current was measured in a standard diode which correlated with a low EL efficiency (2).…”

Oxygen Gettering in Green GaP : N LED's Grown by Overcompensated LPE

“…The results are listed in et al (6) that epilayers grown by overcompensation Table III. Diode efficiency.--The external EL quantum efficiency of various diodes was determined on fabricated structures which had an evaporated contact similar to the one described by Schumaker et al (26) for red LED's. The 20 X 20 mil die was shaped by Jaser scribing, mounted on a TO-18 header, and encapsulated in a high refractive index epoxy.…”