We describe a novel magnetotunneling spectroscopy technique for probing the complicated dispersion curves of hole states in the quantum well of p-type double-barrier resonant-tunneling structures. Strong mixing between light-and heavy-hole states is observed. Some of the states clearly exhibit a negative hole effective mass for motion in the plane of the quantum well.PACS numbers: 73.20.Dx, 73.40.Gk In bulk semiconductors, the low-energy dispersion curves of the light-and heavy-hole valence bands are parabolic. 1,2 However, when a quantizing magnetic field (Bllz) is applied to a bulk semiconductor, the quantized hole energies, or Landau levels, are complicated functions of wave-vector component k z . 1_3 A confining quantum-well potential also produces complicated hole dispersion curves as a function of the in-plane wavevector component k\u even at zero magnetic field. 4-7 In both cases the complexity is due to the admixing of light-hole (LH) and heavy-hole (HH) states due to the spin-orbit interaction. There have been relatively few experimental investigations of the hole dispersion curves in quantum wells because spectroscopic techniques tend to average over k space.In this Letter we describe a novel experimental technique, namely, resonant magnetotunneling spectroscopy, for probing directly the resonant-magnetotunneling spectroscopy, for probing directly the dispersion curves of holes in a quantum well. We study the effect of a large magnetic field applied parallel to the plane of the barriers on the current-voltage characteristics, I(V), of ptype double-barrier resonant-tunneling structures. Tunneling holes acquire a large k\\ due to the magnetic field. The resulting shift in the voltage positions of the resonant peaks in I(V) reveals the light-hole-heavy-hole admixing and shows clearly that some states correspond to a negative hole effective mass for motion in the plane of the quantum well; i.e., increased hole momentum in the plane of the barriers corresponds to decreased kinetic energy. Some evidence of light-hole-heavy-hole mixing has been reported in a previous study of resonant tunneling in the p-type GaAs/AlAs system. 8 Recent calculations 9 of hole states in resonant-tunneling devices have shown that the complicated nature of the valence band strongly influences I(V).Here we consider two devices grown by molecularbeam epitaxy. The composition and valence-band-bending diagram of device 1 at an applied voltage V are shown schematically in Fig.

Hexagonal boron nitride (h-BN) is an attractive van der Waals material for studying fluorescent defects due to its large bandgap. In this work, we demonstrate enhanced pink color due to neutron irradiation and perform electron paramagnetic resonance (EPR) measurements. The new point defects are tentatively assigned to doubly-occupied nitrogen vacancies with (S = 1) and a zero-field splitting (D = 1.2 GHz). These defects are associated with a broad visible optical absorption band and near infrared photoluminescence band centered at ~ 490 nm and 820 nm, respectively. The EPR signal intensities are strongly affected by thermal treatments in temperature range between 600 to 800ºC, where also the irradiation-induced pink color is lost. Our results are important for understanding of point defects in h-BN and their deployment for quantum and integrated photonic applications.