Mikael Malmkvist

Thermal emission of electrons from selected s-shell configurations in InAs/GaAs quantum dots

The thermal emission of electrons from self-assembled InAs/GaAs quantum dots, prepared by molecular-beam epitaxy, with an average base/height size of 20 nm/11 nm in Schottky diodes has been investigated using deep level transient spectroscopy (DLTS). By applying an appropriate set of voltage pulses across the Schottky diode, the two different s-electron configurations have been investigated separately. This avoids the problem of interference between overlapping peaks in DLTS data. We find that a difference in activation energy for the thermal electron emission between the two configurations agrees with expected variation in electron energy levels due to the size distribution of the quantum dots.

Electron capture cross sections of InAs/GaAs quantum dots

By measuring the thermal emission rates of electrons from InAs∕GaAs quantum dots, capture cross sections in the extremely high region of 10−11–10−10cm2 have been found. These data have been confirmed by using an additional method based on a static measurement at thermal equilibrium, where the Fermi level is positioned at the free energy level of the quantum dot s shell.

Electrical Characterization and Small-Signal Modeling of InAs/AlSb HEMTs for Low-Noise and High-Frequency Applications

Electrical characterization and modeling of 2 times 50 mum gatewidth InAs/AlSb HEMTs with 225 nm gate-length have been performed. The fabricated devices exhibited a transconductance gm of 650 mS/mm, an extrinsic cutoff frequency fT and an extrinsic maximum frequency of oscillation fmax of 120 and 90 GHz, respectively, already at a low VDS of 0.2 V. A minimum noise figure less than 1 dB between 2-18 GHz was achieved at a dc power consumption of only 10 mW/mm. This demonstrates the potential of InAs/AlSb HEMTs for low-power, low-noise applications. To account for the elevated gate-leakage current lG in the narrow-bandgap InAs/AlSb HEMT, the conventional field-effect transistor small-signal model has been extended. The relatively high IG was modeled by shunting both Cgs and Cgd with Rgs and .Rgd, respectively. As a result, the small-signal S-parameters were more accurately modeled, especially for frequencies below 10 GHz. Utilizing this modeling approach, excellent agreement was obtained between measured and modeled S-parameters, unilateral power gain U (Masons gain) and stability factor K.

Gate-Recess Technology for InAs/AlSb HEMTs

The gate-recess technology for Si delta-doped InAs/AlSb high-electron-mobility transistors (HEMTs) has been investigated by combining atomic force microscopy (AFM) inspection of the gate-recess versus time with electrical device characterization. Deposition of the gate metal on the In0.5Al0.5As protection layer or on the underlying AlSb Schottky layer resulted in devices suffering from high gate-leakage current. Superior dc and high frequency device performance were obtained for HEMTs with an insulating layer between the gate and the Schottky layer resulting in a reduction of the gate leakage current IG by more than two orders of magnitude at a drain-to-source voltage VDS of 0.1 V. The existence of this intermediate insulating layer was evident from the electrical measurements. AFM measurements suggested that the insulating layer was due to a native oxidation of the AlSb Schottky layer. The insulated-gate HEMT with a gate length of 225 nm exhibited a maximum drain current ID higher than 500 mA/mm with good pinchoff characteristics, a dc transconductance gm of 1300 mS/mm, and extrinsic values for cutoff frequency fT and maximum frequency of oscillation fmax of 160 and 120 GHz, respectively.

Epitaxial Optimization of 130-nm Gate-Length InGaAs/InAlAs/InP HEMTs for High-Frequency Applications

In this paper, the influence of epitaxial-layer design on high-frequency properties of 130-nm gate-length InGaAs/ InAlAs/InP high-electron-mobility transistors (InP HEMTs) has been investigated. The In channel content ([In]: 53%, 70%, and 80%), the J-doping concentration (delta: 3, 5, and 7times10¹² cm^-2), and the Schottky-layer thickness (d_SL: 9,11, and 13 nm) have been varied. The maximum frequency of oscillation f_max, the cutoff frequency f_T, the drain-to-source current JDS, and the transconductance g_m have been analyzed for InP HEMTs. All devices exhibited an increase in I_DS with increasing [In], delta, and d_SL. An increase in f_max, f_T, and g_m were observed with increasing [In]. When changing [In] from 53% to 80%, f_T and f_max improved by 14% and 21%, respectively. For the delta parameter, an increase in f_T and g_m. was found. However, f_max was drastically reduced for the highest delta. This is suggested to be due to the formation of a parasitic conduction channel located at the doping plane in the HEMT structure for delta > 6.3 times 10¹² cm^-2. For the d_SL parameter, an optimum with respect to f_max, f_T, and g_m. was observed. The optimized HEMT exhibited an extrinsic f_T and f_max of 250 and 300 GHz, respectively.

(Cl2:Ar) ICP/RIE Dry Etching of Al(Ga) Sb FOR AlSb/InAs HEMTs

Dry etching of AlSb and Al_0.80Ga_0.20Sb has been performed by inductively coupled plasma/reactive ion etching based on a (Cl₂:Ar) gas mixture without addition of BCI₃. The dry etch process has been used to fabricate AlSb/InAs high electron mobility transistors isolated by a shallow mesa. Good DC/RF results, with extrinsic f_T/f_max= 135/105 GHz, have been measured for a 2times50 mum HEMT with a gate length of 295 nm.

DC characteristics of InAs/AlSb HEMTs at cryogenic temperatures

The DC properties of 110-nm gate-length InAs/AlSb-based HEMTs at cryogenic (30K) and room temperature (300K) have been investigated. Compared to 300K, devices at 30 K exhibited lower on-resistance (R<inf>ON</inf>) and output conductance (g<inf>DS</inf>), a higher transconductance (g<inf>m</inf>) and a more distinct knee in the I<inf>DS</inf>(V<inf>DS</inf>) characteristics. The improvement in the DC performance at cryogenic temperature should mainly be attributed to the lower source-drain resistance.

AlSb/InAs HEMTs on InP substrate using wet and dry etching for mesa isolation

In this paper, we present experimental results on AlSb/InAs HEMTs with deep and shallow mesa using wet and dry etching techniques respectively. Similar electrical results have been obtained using both techniques.

Epitaxial Optimization of 130-nm Gate-Length InGaAs/InAlAs/InP HEMTs for Low-Noise Applications

The epitaxial structure of 130- nm gate-length InGaAs/InAlAs/InP high electron mobility transistors (HEMTs) has been studied in order to optimize the device performance when biased under low-noise conditions. Three essential epitaxial parameters have been varied: the In channel content ([In]: 53%, 70%, and 80%), the delta-doping concentration (delta: 3, 5, and 7 times 10¹² cm^-2), and the Schottky layer thickness (d_SL: 9,11, and 13 nm). All HEMTs exhibited low gate-leakage current I_G below 1 muA/mm at a low-noise bias, except d_SL = 9 nm due to a too thin Schottky layer thickness. It was verified that the lowest noise figure NF was achieved when the square root of the drain-to-source current I_DS over transconductance g_m exhibited a minimum. A clear optimum for both d_Sl and delta was observed with respect to minimum noise figure NF_min. Increasing [In] only provided a slight reduction in N-F_min. In contrast, the RF performance was much more affected by increasing [In]. The lowest NF_min was achieved with a delta doping of 5 times 10¹² cm² and a d_SL of 11 nm.

Effect of Schottky layer thickness on DC, RE and noise of 70-nm gate length InP HEMTs

The Schottky layer thickness of 70-nm InP HEMTs has been studied with respect to DC, RF and noise performance. An optimum gate-to-channel distance between 13-14 nm was found. Biased at a drain-to-source voltage of 0.7 V, a 2times50 mum device exhibited an extrinsic transconductance, gm, of 1.1 mS/mm. The maximum frequency of oscillation, fmax, and the transit frequency, fT, were extracted to 200 GHz and 170 GHz, respectively. A 50 Omega noise temperature of 140 K was measured at room temperature