D. V. Kuksenkov

Low noise p-π-n GaN ultraviolet photodetectors

We report on the fabrication and characterization of p-π-n GaN ultraviolet detectors. The peak responsivity at ∼363  nm is measured to be 0.1 A/W in the photovoltaic mode, and 0.14 A/W with a bias of −15 V. Speed measurements have shown the photoresponse to be RC-limited with the response time decreasing from 17.4 ns at zero bias to 10.3 ns at −6 V bias. For a 200×200 μ m2 device, we measure the dark current to be 2.7 pA at −3 V bias, and a noise density of less than 10−25 A2/Hz, the noise floor of the measurement. Extrapolating the noise data taken at higher reverse biases, we estimate the noise equivalent power to be 6.6×10−15 W/Hz1/2.

VISIBLE-BLIND GAN SCHOTTKY BARRIER DETECTORS GROWN ON SI(111)

We report novel GaN detectors grown by molecular beam epitaxy on Si(111) substrates. Wurtzite structure epitaxial GaN exhibits room-temperature photoluminescence with a band-edge-related emission width as narrow as 7 nm and intensities comparable to high quality layers grown on sapphire by metalorganic chemical vapor deposition. Spectral response of lateral geometry Schottky detectors shows a sharp cutoff at 365 nm with peak responsivities of ∼0.05 A/W at 0 V, and ∼0.1 A/W with a −4 V bias. The dark current is ∼60 nA at −2 V bias. The noise equivalent power is estimated to be 3.7×10−9 W over the response bandwidth of 2.2 MHz.

Schottky barrier photodetectors based on AlGaN

We report solar-blind AlxGa1−xN photovoltaic detectors with cutoff wavelengths as short as 290 nm. Mesa geometry devices of different active areas are fabricated and characterized for spectral responsitivity, speed, and noise performance. The responsivity of the devices near the cutoff wavelength is 0.07 A/W. The detector noise is found to be 1/f limited, with a noise equivalent power of 6.6×10−9 W over the total response bandwidth of 100 kHz.

Origin of conductivity and low-frequency noise in reverse-biased GaN p-n junction

We study the origins of conductivity and low-frequency noise in GaN p-n junctions under reverse bias. Carrier hopping through defect states in the space charge region is identified as the main mechanism responsible for low bias conductivity. Threading dislocations appear the most likely source of such defect states. At higher bias hopping is supplemented with Poole–Frenkel emission. A relatively high level of 1/f-like noise is observed in the diode current. The bias and temperature dependencies of the noise current are investigated.

Low-frequency noise in AlGaN/GaN heterostructure field effect transistors

We report low-frequency noise characteristics of doped-channel GaN/AlGaN heterostructure field-effect transistors grown on sapphire substrates. In the frequency range 1 Hz-100 kHz the observed noise is of the 1/f character. The Hooge constant is of the order of 10/sup -2/ and is linearly proportional to the channel width. The noise originates in the fluctuation of carrier number in the channel due to relatively high density of defects at the GaN/AlGaN heterointerface.

Spontaneous emission factor in oxide confined vertical-cavity lasers

We report on measurements of the spontaneous emission factor for oxide-confined InGaAs vertical cavity surface emitting lasers. The spontaneous emission factor is determined as a function of the active layer volume from the measurement of small-signal harmonic distortion at threshold. For a 3×3 μm oxide aperture device we obtain spontaneous emission factor of 4.2⋅10−2 at room temperature.

Differential carrier lifetime in oxide-confined vertical cavity lasers obtained from electrical impedance measurements

Differential carrier lifetime measurements were performed on index-guided oxide-confined vertical cavity surface emitting lasers operating at 980 nm. Lifetimes were extracted from laser impedance measurements at subthreshold currents, with device size as a parameter, using a simple small-signal model. The carrier lifetimes ranged from 21 ns at 9 μA, to about 1 ns at a bias close to threshold. For a 6×6 μm2 oxide aperture device the threshold carrier density was nth∼2×1018 cm−3. The effect of carrier diffusion was also considered. An ambipolar diffusion coefficient of D∼11 cm2 s−1 was obtained.

Low-frequency noise and performance of GaN p-n junction photodetectors

We report on low-frequency noise characteristics of visible-blind GaN p-n junction photodetectors. Carrier hopping through defect states in the space charge region, believed to be associated with dislocations, is identified as the main mechanism responsible for the dark conductivity of the photodiodes. The dark current noise has the 1/f character and obeys the Hooge relation with /spl alpha//spl ap/3.

Small-signal impedance characteristics of quantum-well laser structures

Small-signal impedance characteristics of quantum-well laser structures are analyzed. A simple analytical expression for the frequency dependence of below-threshold small-signal impedance is derived and verified experimentally. It is shown that the differential carrier lifetime and quantum-well transport and capture times can be extracted from electrical impedance measurements.

Carrier lifetimes in vertical cavity surface emitting lasers determined from electrical impedance measurements

Summary form only given. Differential carrier lifetimes of index-guided oxide-confined (980 nm) vertical cavity surface-emitting lasers (VCSELs) were obtained from laser impedance measurements at subthreshold currents and equivalent circuit modeling.