Physical properties and efficiency of GaNP light emitting diodes

Abstract

GaNP / GaP is promising for yellow-amber-red light emitting diodes ͑LEDs͒. In this study, pressure and temperature dependent electroluminescence and photocurrent measurements on bulk GaP / GaN 0.006 P 0.994 / GaP LED structures are presented. Below ϳ110 K, emission is observed from several localized nitrogen states. At room temperature, the band-edge energy increases weakly with pressure at a rate of +1.6 meV/ kbar, substantially lower than the ⌫ band gap of GaP ͑+9.5 meV/ kbar͒. Thus, despite the multiplicity of nitrogen levels, the band anticrossing model reasonably describes this system based on an average of the nitrogen states. Furthermore, carrier leakage into the X minima of GaP reduces the efficiency in GaNP-LEDs with increasing pressure. For a number of years, nitrogen has been added to the indirect semiconductor GaP to act as a radiative defect center to produce light emitting diodes ͑LEDs͒.1 Recently, there has been renewed interest in III-V-N semiconductors due to the large band-gap bowing that is observed in such materials when only a few percent of nitrogen is added. The interaction between the localized N states and the conduction band ͑CB͒ minimum has been effectively modeled with both the band anticrossing ͑BAC͒ model 2 and the empirical pseudopotential method.3 This has recently led to activity in dilute nitrides based on GaP where the fraction of nitrogen can be carefully controlled via molecular beam epitaxy ͑MBE͒ growth. Additionally, yellow-amber-red GaNP LEDs may offer better device characteristics than current AlInGaP devices due to a weaker dependence of the band gap 4 and lower thermal resistivity. 5 In this letter, we investigate the validity of a simple BAC model in GaNP-based materials and consider the factors limiting the electro-optic efficiency of LEDs based on GaNP.The devices studied here were grown by MBE and utilize simplified chip processing by one-step growth on transparent 350 m thick n-type GaP ͑100͒ substrates. The epitaxial layers consist of a 0.3 m thick n-GaP layer ͑Si doped͒, 0.15/ 0.1/ 0.15 m thick undoped GaP / GaN 0.006 P 0.994 / GaP active region, and 0.8 m thick p-GaP ͑Be doped͒ contact layer. LED chips were fabricated using Ge/ Au/ Ni/ Au and AuZn metallization for n-and p-type contacts, respectively.We employ temperature dependent measurements performed with a standard closed cycle cryostat setup over the temperature range of 70-300 K. This gives temperature and current dependencies of the electroluminescence ͑EL͒ spectra. The application of high hydrostatic pressure causes an increase in the direct band gap, and a reduction in the indirect X minima, thereby allowing investigations of the band structure and leakage effects into the indirect minima of GaP. Pressure dependent measurements were performed over the range of 0 -10 kbar using gaseous helium as the pressure medium. In the dilute nitrides, high pressure can also be used to tune the interaction between the nitrogen level͑s͒ and the conduction band of the host material, forming a useful means of investiga...

Temperature dependence and physical properties of Ga(NAsP)/GaP semiconductor lasers

“…E N was found from interpolation of the isolated nitrogen level in GaAs and GaP and has been assumed to have a negligible pressure dependence. 16 It is clearly seen in Fig. 1 that the BAC model gives good agreement with the experimental data for which C MN = 1.9 eV.…”

“…Hence we conclude that the leakage level has a slightly smaller pressure dependence than the CB quasi-Fermi level. This suggests that leakage into the X minima of the indirect barriers ͑as previously observed in shorter wavelength GaNP light emitting diodes 16 ͒ is not significant here, as the leakage level would then have a negative pressure coefficient. In summary, we have found that the BAC model can well describe the band gap of GaNAsP/GaP as a function of pressure.…”

“…It is therefore instructive to see if the BAC model can explain this reduced pressure dependence, as has been the case for other dilute nitride materials. 16 In the BAC model, the interaction between a localized N state and extended CB states splits the CB into two subbands, E + and E -. Their energies are described by the following equation:…”

Atomistic calculations of Ga(NAsP)/GaP(N) quantum wells on silicon substrate: Band structure and optical gain

“…The C CB is found above the Xxy CB for all composition range, in agreement with the results of Prieto et al 26 for the case of GaAs strained layer on GaP(001) which is observed slightly indirect near the X-point. The N-level is insensitive to strain as in reported previous works 27,28 and lies below the CB of strained GaAsP whatever the content. Fig.…”

Dilute nitride InNP quantum dots: Growth and photoluminescence mechanism

“…However, recent development in light emitting diodes (LEDs) 1 and water splitting, 2 taking advantage of its transparency and band energy levels, raised interests in materials based on the GaP platform. The small difference in the lattice constants between GaP and Si (5.451 Å and 5.431 Å , respectively) also provides a III-V-on-Si integration opportunity.…”