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Title: Efficiency limitations and band anti-crossing in novel dilute nitride optoelectronic devices
Author: Chamings, James
ISNI:       0000 0004 2673 1717
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2009
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The dilute nitrides on GaAs (e.g. Ga(In)NxAs1-x where typically x < 5%) have provided a large amount of interesting physics and led to the development of improved telecommunication lasers. In the last 5 years, novel dilute nitride materials (such as GaN(As)P) have grown in popularity due to applications such as monolithic growth on silicon and improved device characteristics in red-amber-yellow solid state illumination. The Band Anti-Crossing model, using a single weighted nitrogen level (found through photocurrent spectroscopy), is found to successfully predict the band gap energy in GaNP/GaP and GaNAsP/GaP and bulk GaInNAs/GaAs with nitrogen composition, temperature and high hydrostatic pressure. An investigation over a range of host materials found that the coupling parameter can be modelled in terms of the energy separation between the host conduction band minimum and the nitrogen level. GaNAsP/GaP single quantum well lasers are a realistic possibility for an efficient laser source grown on silicon for monolithic optoelectronic integrated circuits. Large threshold current densities of over 0.75kA/cm2 at 80K and 890nm and large temperature variations in the threshold current are shown to be due to non-radiative loss processes. Low characteristic temperatures of the threshold current and differential efficiency (T0=60K and T1=30K at 130K) are found. The sub-linear dependence of the spontaneous emission vs current curve and increasing threshold current with high pressure reveal this loss process is carrier leakage. It is shown that the leakage is not into the X-minima of the GaP barriers, but associated with nitrogen levels in the GaP barriers. If this leakage path can be eliminated, a low room temperature threshold current density should be achieved. (In)GaNP/GaP LEDs are studied for use in red-amber-yellow illumination applications. Through high pressure measurements, it is found that 90 +/-10% of the current flowing through a GaN0.006P0.994 bulk LED is lost to carrier leakage at room temperature and pressure, at a current density of 40A/cm2. When using an In0.14Ga0.86N0.006P0.994 quantum well (of thickness 100 A) active region, the electron potential barrier is increased and carrier leakage accounts for 50+/-15% of the device current density (40A/cm2) at room temperature and pressure. At 100K it was found the leakage reduces to below 10% at current density of 40A/cm2 in all devices. If the leakage path can be reduced, these devices may offer better device characteristics than current red AlInGaP LEDs. Initial investigations on bulk GaInNAs avalanche photodiodes show that with an increase of nitrogen concentration and reduction in band gap, the breakdown voltage increases, consistent with the nitrogen suppressing electron impact ionization as predicted by theory. The pressure coefficient of the breakdown voltage in GaInNAs was found to be larger in magnitude and opposite in sign (dVbd/dP=+5.5+/-0.5 x10-3kbar-1) than the pressure coefficient of the breakdown voltage in GaAs, showing that nitrogen induces a profound change in the carrier scattering mechanisms, which may provide low-noise, high sensitivity detectors at telecommunication wavelengths.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available