High-quality AlN∕GaN-superlattice structures for the fabrication of narrow-band 1.4 μm photovoltaic intersubband detectors

Abstract

We report on high-quality short-period superlattices in the AlN/ GaN material system. Thanks to significant advances in the epitaxial growth, up to 40 superlattice periods with a total layer thickness of 120 nm could be grown without cracking problems. Given an intersubband transition energy on the order of 910 meV, these superlattices could be used as room temperature, narrow-band, photovoltaic detectors for wavelengths around 1.4 m. In photovoltaic operation, the full width at half maximum is as narrow as 90 meV, underlining the high quality of the interfaces and the single layers in our structures.Recently, there has been increasing interest in III-nitride semiconductors for fabrication of ultrahigh-speed intersubband ͑ISB͒ devices. 1 Because of the large conduction band discontinuity of nearly 2 eV between AlN and GaN, this material combination is suitable for ISB transitions with an energy difference of roughly 1 eV. 2 Since such a large photon energy covers the technologically interesting wavelength region around 1.3/ 1.55 m, passive or active modulators and photodetectors for telecommunication applications can be envisioned. It is expected that the ultrafast recovery time of such ISB transitions ͑150-370 fs, depending on the refer-ence͒ will eventually result in high-speed devices in the Ͼ10 GHz range. 3,4 Shortly after the demonstration of ISB absorption in both quantum well ͑QW͒ and quantum dot superlattices ͑SLs͒, 5,6 several prototypes of QW and quantum dot ISB detectors have been published. 7-9 However, all devices reported so far, and in particular the QW-based ISB photodetectors ͑QWIPs͒, had relatively broad detection peaks ͓full width at half maximum ͑FWHM͒ considerably larger than 100 meV for ISB energies in the 800 meV range͔. This broadening is mainly due to interfacial roughness and might be augmented by drift of the growth rate during the epitaxy. Recently, improved deposition techniques based on the use of In as a surfactant during epitaxial growth of AlGaN, GaN, and AlN layers have resulted in significantly smoother surfaces, and therefore a better interface quality. 10 In this letter, we present a series of QWIP samples with a nominally identical active region, i.e., the same QW and barrier layer thickness, and differing in the doping level in the QWs and the thickness of the cap layer only. All samples present extremely narrow ͑FWHM ϳ90 meV͒ TM-polarized absorption/detection spectra at an ISB transition wavelength around 1.4 m, which demonstrates both improved crystalline quality of the layers and interfaces and high reproducibility of the growth process. QWIP structures consist of 40 periods of 1.0-nm-thick Si-doped GaN QWs with 2.0-nm-thick AlN barriers, grown by plasma-assisted molecular-beam epitaxy ͑PAMBE͒ on 1m-thick AlN-on-sapphire substrates. Active nitrogen was provided by a radio-frequency plasma cell, and standard effusion cells were used for Ga, Al, Si, and In. The doping level in the GaN QWs was 5 ϫ 10 19 cm −3 for sample E728 and 1 ϫ 10 19 cm −3 for E739 and E740. Prior to th...

Latest developments in GaN-based quantum devices for infrared optoelectronics

“…This extremely narrow peak confirms the good structural material quality. Typical responsivity values for samples with 40 GaN/AlN periods are about 8 lV/W [20].…”

Monolithically integrated UV/IR‐photodetectors based on an AlN/GaN‐based superlattice grown on an AlGaN buffer layer

“…This will have a positive effect on the acquisition speed of large multi-spectral images. Our solution is based on the monolithic integration of a photoconductive UV interband detector based on an AlGaN thin film [9] and a photovoltaic near-IR intersubband detector based on an AlN/GaN superlattice [10][11][12]. As a first demonstrator, we present here a UV/IR detector pair with only 350 µm spatial separation between the UV and IR device.…”

III-Nitride Nanostructures for Infrared Optoelectronics

“…Furthermore, in situ monitorization of the surface morphology by reflection high energy electron diffraction (RHEED) makes possible to control the growth at the atomic layer scale. Room temperature ISB absorption at λ ≈ 1.3−1.55 has been demonstrated in both QW [4][5][6][7][8] and QD superlattices [9][10][11], and several prototypes of ISB detectors [12][13][14][15] and electro-optical modulators [16] have recently been reported. These developments are possible thanks to improved deposition techniques for Al(Ga)N/GaN layers and superlattices [17][18][19].…”