Density-of-states distribution in AlGaN obtained from transient photocurrent analysis

Niehus, M.; Schwarz, R.; Koynov, S.; Heuken, M.; Meister, D.; Meyer, B. K.; Main, C.; Reynolds, S.

doi:10.1016/s0921-5107(00)00773-x

Cited by 6 publications

(2 citation statements)

References 3 publications

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“…4-6. The exponents in the power law decay are around --0.3 in accordance with samples grown by other techniques [9]. Similar phenomena with different values for the power law index occur in amorphous semiconductors such as a-Si : H. As an explanation for the long times the presence of extended band tail states was invoked [10].…”

Section: Resultssupporting

confidence: 80%

Low Temperature Photoluminescence, Transient Photoconductivity and Microwave Reflection for Optical Properties and Transport in PLD‐GaN

Niehus¹,

Sanguino²,

Schwarz³

et al. 2002

phys. stat. sol. (c)

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Optical and transport data on GaN samples grown by low-temperature pulsed laser deposition are presented. Large below-gap band tails are observed in optical absorption spectroscopy. The most intense photoluminescence lines of medium crystalline quality samples can be attributed to excitons bounded to stacking faults. The samples of the highest quality show, besides the ubiquitous yellow band, a large near band emission (NBE) peaking at 3.47 eV. The large width of the NBE is attributed to the joint effects of the band tails and an elevated carrier concentration. Secondary photocurrent transients show a slow decay reaching the millisecond time region for a variety of excitation wavelengths and intensities, with a power law decay exponent of around --0.3. The long times are attributed to the trapping of excess carriers in extended band tail states. From the comparison of photocurrent decay with excess carrier-induced microwave reflection it is concluded that the decay dynamics at the air/film and film/substrate interfaces are identical.Introduction GaN is one of the base materials for modern electronic and optoelectronic devices such as light emitting diodes (LEDs), solar blind UV detectors, laser diodes (LDs) or high-mobility electron transistors (HEMTs) [1]. Despite impressive technical advances, some basic materials issues remain to be resolved. One of these is the elevated density of unwanted impurities that appear in the material independently of the deposition technique. The metalorganic chemical vapour deposition (MOCVD) technique, for instance, relies always on a precursor gas that may introduce unwanted effects.We presented recently a new approach for depositing GaN films, a hybrid, two-step, low-temperature pulsed laser deposition (PLD) [2]. In this work we study the optical properties and transport in gallium nitride (GaN) deposited by this technique. Optical spectroscopy (transmission and photoluminescence measurements) and photoconductivity data are presented.

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Section: Resultssupporting

confidence: 80%

Low Temperature Photoluminescence, Transient Photoconductivity and Microwave Reflection for Optical Properties and Transport in PLD‐GaN

Niehus¹,

Sanguino²,

Schwarz³

et al. 2002

phys. stat. sol. (c)

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“…4 (colour). Subbandgap luminescence and photoconductivity of Al 0.18 GaN/GaN at 300 and 500 K Transient Photoconductivity (TPC) The slow decay in transient photoconductivity, which follows a power law with an index around 0.3 over several orders of magnitude is known for bulk GaN [4]. We measured the photoconductivity frequency dependence of our samples for above and below bandgap excitation.…”

Section: Samples and Experimental Techniquesmentioning

confidence: 99%

Photoconductivity Studies of Al0.18Ga0.82N/GaN Single Heterostructure

Niehus¹,

Schwarz²,

Koynov³

et al. 2001

phys. stat. sol. (a)

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We present spectral photoconductivity (SPC) and transient photoconductivity (TPC) studies in a Al 0.18 Ga 0.82 N/GaN single heterostructure. We attribute near bandgap peaks in the SPC between 300 and 500 K to a deep trap-conduction band transition. The trap distribution lies approximately 100 meV above the valence band edge, for both GaN and AlGaN layers. In TPC studies we show that charge buildup after strong pulsed laser excitation can be detected by anomalous photocurrent decay.

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