GaN/AIGaN intersubband optoelectronic devices (original) (raw)

This paper reviews recent progress toward intersubband (ISB) devices based on III-nitride quantum wells (QWs). First, we discuss the specific features of ISB active region design using GaN/AlGaN materials, and show that the ISB wavelength can be tailored in a wide spectral range from near-to long infrared wavelengths by engineering the internal electric field and layer thicknesses. We then describe recent results for electro-optical waveguide modulator devices exhibiting a modulation depth as large as 14 dB at telecommunication wavelengths. Finally, we address a new concept of III-nitride QW detectors based on the quantum cascade scheme, and show that these photodetectors offer the prospect of high-speed devices at telecommunication wavelengths. for control-by-design devices relying on quantum wells (QWs) or quantum dots (QDs). One famous example is the quantum cascade laser (QCL), which was invented in the mid-1990s at Bell Laboratories . Using materials such as GaAs/AlGaAs, InGaAs/AlInAs or antimonides, ISB devices such as the QCLs can be tuned from the mid-infrared to the THz spectral range. Operation at short wavelengths is limited by the available conduction band offset and by the material transparency. III-nitride semiconductors (GaN, AlN, InN and their alloys) are attracting much interest for ISB devices operating in the near-infrared spectral range and, in particular, in the 1.3-1.55 µm wavelength window used for fiber optic telecommunications. Not only are they transparent in a wide spectral region (360 nm to 13 µm for GaN), but the conduction band offset provided by their heterostructures is quite large, being of the order of 1.75 eV for GaN/AlN . In contrast to InAs/AlSb materials, which also exhibit a large conduction band discontinuity, the remote valleys of GaN lie very high in energy (>2 eV above the point [4]), offering the potential for ISB light-emitting devices at record short near-infrared wavelengths. Another specificity of nitride materials is substantial longitudinal-optical (LO) phonon energy (92 meV for GaN), as well as the presence of huge internal fields induced by spontaneous and piezoelectric polarizations along the c-axis, inherent in their wurtzite structure. Due to the rather heavy electron effective mass (0.22 × m 0 for GaN), ultrathin QW or QD layers, typically 1-1.5 nm thick, are required in order to tune the ISB wavelength in the 1.3-1.55 µm range.