Electronic structure near the band gap of heavily nitrogen doped GaAs and GaP

Abstract

Isoelectronic impurity nitrogen atoms have been found to generate a series of localized states in GaP and GaAs. These states can be either bound (within the band gap) or resonant (above the band gap) when in the dilute doping limit (roughly < 1019 cm−3 for GaP and < 1018 cm−3 for GaAs). With increasing nitrogen doping level, a shift of the absorption edge from the binary band gap has been observed for the so-called GaPN or GaAsN alloy. We discuss the similarity and dissimilarity between the two systems in the following aspects: (1) How does the nitrogen doping perturb the host band structure? (2) How do the nitrogen bound states evolve with increasing nitrogen doping level? (3) What are the dominant contributors to the band edge absorption? And (4) does a universal model exist for GaPN and GaAsN? Other issues that will be discussed are: how does one define the band gap for these materials, and what is the relevance of various theoretical band structure calculations to the experimentally measured parameters.

Evolution of the electron localization in a nonconventional alloy system GaAs1−xNx probed by high-magnetic-field photoluminescence

“…However, starting from around 10 T, at the high-energy edge of the spectrum, an additional feature ͑at ϳ1.47 eV for the 0.1% sample, and at ϳ1.44 eV for the 0.22% sample͒ emerges with increasing magnetic field, and becomes a well-developed peak at 30 T. Its peak energy is close to but always lower than the excitonic band gap ͑the excitonic band gap has been found to be ϳ1.475 and ϳ1.442 eV for the xϭ0.1% and 0.22% samples, respectively͒. 6,16 This additional PL feature, hereafter referred to as G, exists for all the dilutely doped samples ͑with xϽ0.7%) studied in this work. Right below the dominant G-line, there are other features as well ͑two for 0.1% sample, and one for 0.22% sample͒ that seem to change with the applied magnetic field.…”

“…1,2 A lot of experimental and theoretical investigations have been carried out to study the origin of this giant bandgap reduction. [3][4][5][6][7][8][9][10][11] It is generally understood that in the dilute doping limit, N impurities introduce highly localized states either above or below the conduction band edge of GaAs. These impurity states, originating from isolated N atoms, N pairs, and N clusters, have progressively lower energy levels in GaAs and emerge sequentially with increasing doping of nitrogen.…”

“…However, the exact nature of those bound states or emission lines and their evolutions with increasing nitrogen doping remain unclear. 6,7,14,15 In order to better understand the nature of various nitrogen-induced bound states, the impurity-host interaction, and to what extent the wisdom for conventional alloys is still applicable to this ''unconventional'' alloy system, we have carried out systematic magneto-photoluminescence ͑PL͒ measurements on a set of GaAs 1Ϫx N x samples ͑with x ranging from 0.1% to 2.5%͒ in magnetic fields up to 30 T. The biggest advantage of performing magneto-PL measurements at high magnetic fields is that this technique can clearly distinguish the extended states and localized states without any ambiguity. The samples were grown by gas-source molecular-beam epitaxy on semi-insulating ͑001͒ GaAs substrates at 420°C and a growth rate of 0.8 m/h using a rf nitrogen radical beam source with a mixture of N 2 and Ar in a ratio of 1:9.…”

Comparative studies of optoelectrical properties of prominent PV materials: Halide perovskite, CdTe, and GaAs

“…Also note that the excitonic bandgaps determined by different techniques are consistent with each other typically within a few meV for a high purity conventional semiconductor. For instance, for the same piece of the GaAs sample that yielded the excitonic absorption peak at 1.425 eV shown in Figure 2(b), modulation spectroscopy resulted in a bandgap of 1.422 eV [59]; for single crystalline CdTe, modulation spectroscopy resulted a bandgap of 1.513 eV [62], also very close to the excitonic bandgap determined by PL [58]. Another important indication of the PL emission being intrinsic in nature is that its peak position and lineshape do not show significant variations with excitation density except for the intensity, which is the case for CdTe and GaAs samples studied in this work.…”

Alloy states in dilute GaAs1−xNx alloys (x<1%)

“…However, Zhang et al proposed that the impurity band formation from N-induced bound states in GaAs:N played a key role in the band gap reduction, 8 and pointed out that the observedscaling rule of band gap reduction was supportive of their argument. 9 A recent study of Zhang et al has indicated that the effect of the impurity band formation on the band edge electronic structure critically depends on the band structure of the host material. 10 Very recently, Wang et al 11 explored a PL emission in GaAsN under high magnetic fields and assigned it as an on-set of delocalized states, resulting from the interaction of localized impurity state and the approaching delocalized host state.…”