The temperature-dependent characteristic of band offsets at the heterojunction interface was studied by an internal photoemission (IPE) method. In contrast to the traditional Fowler method independent of the temperature (T), this method takes into account carrier thermalization and carrier/dopant-induced band-renormalization and band-tailing effects, and thus measures the band-offset parameter at different temperatures. Despite intensive studies in the past few decades, the T dependence of this key band parameter is still not well understood. Reexamining a p-type doped GaAs emitter/undoped Al x Ga 1−x As barrier heterojunction system disclosed its previously ignored T dependency in the valence-band offset, with a variation up to ∼−10 −4 eV/K in order to accommodate the difference in the T-dependent band gaps between GaAs and AlGaAs. Through determining the Fermi energy level (E f), IPE is able to distinguish the impurity (IB) and valence bands (VB) of extrinsic semiconductors. One important example is to determine E f of dilute magnetic semiconductors such as GaMnAs, and to understand whether it is in the IB or VB.

The spectral response of common optoelectronic photodetectors is restricted by a cutoff wavelength limit (λ c) that is related to the activation energy (or band-gap) of the semiconductor structure (or material) (∆) through the relationship: λ c = hc/∆. This spectral rule dominates device design and intrinsically limits the long wavelength response of a semiconductor photodetector. Here, we report a new, long wavelength photodetection principle based on a hot-cold hole energy transfer mechanism that overcomes this spectral limit. Hot carriers injected into a semiconductor structure interact with cold carriers and excite them to higher energy states. This enables a very long-wavelength infrared response. In our experiments, we observe a response up to 55 µm, which is tunable by varying the degree of hot-hole injection, for a GaAs/AlGaAs sample with ∆ = 0.32 eV (equivalent to 3.9 µm in wavelength).

Hole transitions from the heavy-hole ͑hh͒ to the light-hole ͑lh͒ band contributing to the 4-10 m response range are reported on p-GaAs/ AlGaAs detectors. The detectors show a spectral response up to 16.5 m, operating up to a temperature of 330 K where the lh-hh response is superimposed on the free-carrier response. Two characteristic peaks observed between 5-7 m are in good agreement with corresponding energy separations of the lh and hh bands and thus originated from lh-hh transitions. Results will be useful for designing multi-spectral detection which could be realized on a single p-GaAs structure.

We report on the InAs quantum dots (QDs) laser in the 1.55μm wavelength region grown by gas source molecular-beam epitaxy. The active region of the laser structure consists of fivefold-stacked InAs QD layers embedded in the InGaAsP layer. Ridge waveguide lasers were processed and continuous-wave mode operation was achieved between 20 and 70°C, with characteristic temperature of 69K. High internal quantum efficiency (56%) and low infinite length threshold current density (128A∕cm2 per QD layer) was obtained for the as-cleaved devices at room temperature. The lasing wavelength range between 1.556 and 1.605μm can be covered by varying the laser cavity length.